Consolidated Statements of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Common [Member]	Warrant [Member]	Additional Paid in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total
Beginning balace at Dec. 31, 2015	$ 331	$ 946	$ 503,529	$ 233,604	$ 191	$ 738,601
Beginning balace (in shares) at Dec. 31, 2015	33,467,893
Net Income				71,990		71,990
Other comprehensive income (loss)					(1,131)	(1,131)
Stock-based compensation expense			5,159			5,159
Issuance of common stock related to options exercised, net of shares withheld for payroll taxes			282			282
Issuance of common stock related to options exercised, net of shares withheld for payroll taxes (in shares)	23,614
Excess tax benefits from stock compensation			166			166
Vesting of time based stock awards issued at date of grant, net of shares withheld for payroll taxes	$ 2		(2)
Vesting of time based stock awards issued at date of grant, net of shares withheld for payroll taxes (in shares)	(17,556)
Time based stock awards granted (in shares)	104,775
Issuance of common stock related to employee stock purchase plan			572			572
Issuance of common stock related to employee stock purchase plan (in shares)	12,154
Ending balance at Sep. 30, 2016	$ 333	946	509,706	305,594	(940)	$ 815,639
Ending balance (in shares) at Sep. 30, 2016	33,590,880					33,590,880
Beginning balace at Dec. 31, 2016	$ 338		513,531	331,311	(2,381)	$ 842,799
Beginning balace (in shares) at Dec. 31, 2016	34,023,850					34,023,850
Net Income				84,663		$ 84,663
Other comprehensive income (loss)					1,432	1,432
Stock-based compensation expense			4,198	1		4,199
Issuance of common stock related to options exercised, net of shares withheld for payroll taxes	$ 1		258			259
Issuance of common stock related to options exercised, net of shares withheld for payroll taxes (in shares)	60,925
Vesting of time based stock awards issued at date of grant, net of shares withheld for payroll taxes	$ 1		(2)			(1)
Vesting of time based stock awards issued at date of grant, net of shares withheld for payroll taxes (in shares)	(16,962)
Vesting of performance based stock awards, net of shares withheld for payroll taxes (in shares)	3,589
Time based stock awards granted (in shares)	91,097
Issuance of common stock related to employee stock purchase plan			631			631
Issuance of common stock related to employee stock purchase plan (in shares)	11,510
Ending balance at Sep. 30, 2017	$ 340		$ 518,616	$ 415,975	$ (949)	$ 933,982
Ending balance (in shares) at Sep. 30, 2017	34,174,009					34,174,009