Treasury Stock - Additional Information (Details) - USD ($)	12 Months Ended			62 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Nov. 30, 2008
Equity, Class of Treasury Stock [Line Items]
Costs of shares repurchased	$ 7,431,896	$ 6,484,844	$ 927,912
November 2008 Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Repurchase of common stock, authorized amount					$ 8,000,000
Number of shares retired				4,660
Costs of shares repurchased		$ 6,500,000	$ 928,000	$ 105,000
Number of shares repurchased		119,403	25,836
Average price per share		$ 54.31	$ 35.92	$ 22.00
New Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Repurchase of common stock, authorized amount	10,000,000	$ 10,000,000
Costs of shares repurchased	$ 7,400,000
Number of shares repurchased	151,453
Average price per share	$ 49.07