The Gemara on Amud Beis discusses the level of details and explanation that was given along with the written Torah:

רַבִּי יִשְׁמָעֵאל אוֹמֵר כְּלָלוֹת נֶאֶמְרוּ בְּסִינַי וּפְרָטוֹת בְּאֹהֶל מוֹעֵד רַבִּי עֲקִיבָא אוֹמֵר כְּלָלוֹת וּפְרָטוֹת נֶאֶמְרוּ בְּסִינַי וְנִשְׁנוּ בְּאֹהֶל מוֹעֵד וְנִשְׁתַּלְּשׁוּ בְּעַרְבוֹת מוֹאָב

Rabbi Yishmael says: General statements were said at Sinai, i.e., Moses received general mitzvos at Sinai, including the Ten Commandments. And the details of the mitzvot were explained to Moses at a later time in the Tent of Meeting. Rabbi Akiva says: Both general statements and the details of mitzvos were said at Sinai, and later repeated in the Tent of Meeting, and reiterated a third time by Moses to the Jewish people in the plains of Moab. Rabbi Shimon holds in accordance with his teacher, Rabbi Akiva, and counts Mount Sinai and the Tent of Meeting Tent as two distinct places where all of the mitzvos were given.

There is a Sifra (Behar) famously quoted by Rashi, which makes a similar statement: 

בהר סיני. מָה עִנְיַן שְׁמִטָּה אֵצֶל הַר סִינַי? וַהֲלֹא כָל הַמִּצְוֹת נֶאֶמְרוּ מִסִּינַי? אֶלָּא מַה שְּׁמִטָּה נֶאֶמְרוּ כְלָלוֹתֶיהָ וּפְרָטוֹתֶיהָ וְדִקְדּוּקֶיהָ מִסִּינַי אַף כֻּלָּן נֶאֶמְרוּ כְלָלוֹתֵיהֶן וְדִקְדּוּקֵיהֶן מִסִּינַי, כָּךְ שְׁנוּיָה בְּתֹ"כֹּ; וְנִרְאֶה לִי שֶׁכָּךְ פֵּרוּשָׁהּ: לְפִי שֶׁלֹּא מָצִינוּ שְׁמִטַּת קַרְקָעוֹת שֶׁנִּשְׁנֵית בְּעַרְבוֹת מוֹאָב בְּמִשְׁנֵה תוֹרָה, לָמַדְנוּ שֶׁכְּלָלוֹתֶיהָ וּפְרָטוֹתֶיהָ כֻּלָּן נֶאֶמְרוּ מִסִּינַי, וּבָא הַכָּתוּב וְלִמֵּד כָּאן עַל כָּל דִּבּוּר שֶׁנִּדְבַּר לְמֹשֶׁה, שֶׁמִּסִּינַי הָיוּ כֻלָּם, כְּלָלוֹתֵיהֶן וְדִקְדּוּקֵיהֶן, וְחָזְרוּ וְנִשְׁנוּ בְּעַרְבוֹת מוֹאָב:

בהר סיני [AND THE LORD SPOKE UNTO MOSES] ON THE MOUNT SINAI 

What has the matter of the Sabbatical year to do with Mount Sinai that Scripture felt compelled to expressly state where it was commanded? Were not all commandments given on Sinai? But this statement is intended to suggest the following comparison: How is it in the case of the law of Shemittah? Its general rules, [its specific prescriptions] and minute details were ordained on Mount Sinai! So, also, were all commandments with their general rules and their minute details ordained on Mount Sinai. Thus is taught in Torath Cohanim (Sifra, Behar, Section 1 1). It seems to me that the following is the explanation of this: Since we do not find in Deuteronomy that the law concerning “the rest of the soil in the Sabbatical year” was repeated in “the fields of Moab” (cf. Deuteronomy 34:1; the place where Moses repeated many of the commandments contained in the other books of the Pentateuch), we may infer that all its general rules and specific prescriptions must have been promulgated on Sinai. The express mention of בהר סיני here appears therefore to be unnecessary but Scripture by mentioning it intends to teach regarding every Divine command (lit., Divine utterance) that was spoken to Moses that in every case they, their general rules and minute details originated at Sinai and that they were only repeated again in “the fields of Moab”.

Peri Tzaddik (Behar 2) adds a twist to this Peshat. He asks, why did the Torah use Shemittah as the example to teach that all of the laws were given in detail? This could have been done with any mitzvah? Rather, this statement hints at the following. Originally the Jews in the wilderness did not have to worry about material matters, as the Manna provided for every need. Their experience of Torah and life was on a spiritual plane. Thus, the real question was, “What relevance is the observance of a Sabbatical Year to the Jewish people, who did not have to farm or work during any year? The  answer was, actually it was all there from the beginning. The Torah given at Mount Sinai was meant for the Jewish people to live a physical existence combined with the spiritual. Thus, Shemittah is deeply linked to Sinai, as the Jews will utilize the Sabbatical year to reconnect with an intense spiritual life that they enjoyed constantly in the wilderness, but only once every seven years.