Income Taxes - Provision for income taxes (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Current:
Federal									$ 7,688,428	$ 8,709,338	$ 10,187,010
State									1,196,034	1,393,675	1,661,860
Total current									8,884,462	10,103,013	11,848,870
Deferred:
Federal									308,090	1,474,425	598,674
State									47,927	235,940	97,665
Total deferred									356,017	1,710,365	696,339
Income tax expense	$ 2,384,462	$ 2,368,923	$ 2,665,057	$ 1,822,037	$ 2,528,895	$ 2,833,019	$ 2,886,484	$ 3,564,980	$ 9,240,479	$ 11,813,378	$ 12,545,209