Treasury Stock - Additional Information (Details) - USD ($)	6 Months Ended	9 Months Ended	12 Months Ended
	Jun. 30, 2016	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Nov. 30, 2008
Equity, Class of Treasury Stock [Line Items]
Number of shares purchased		273,302	159,873
Costs of shares purchased		$ 13,350,705	$ 7,866,410
Costs of shares repurchased		5,484,295
Odd-Lot Buy-Back Program [Member]
Equity, Class of Treasury Stock [Line Items]
Number of shares purchased			119,403	25,836
Costs of shares purchased			$ 6,500,000	$ 928,000
Repurchase of common stock, authorized amount						$ 8,000,000
Number of shares retired					4,660
Amount of treasury shares retired					$ 105,000
Average price per share			$ 54.31	$ 35.92
New Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Costs of shares purchased		5,500,000
Repurchase of common stock, authorized amount		$ 10,000,000	$ 10,000,000
Number of shares repurchased	113,429
Average price per share		$ 48.35