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				47,467		47,467
Other comprehensive income (loss)					(1,515)	(1,515)
Stock-based compensation			3,312			3,312
Issuance of common stock related to options exercised, net of shares withheld for payroll taxes			252			252
Issuance of common stock related to options exercised, net of shares withheld for payroll taxes (in shares)	21,825
Vesting of restricted stock awards issued at date of grant, net of shares withheld for payroll taxes	$ 2		(2)
Vesting of restricted stock awards issued at date of grant, net of shares withheld for payroll taxes (in shares)	(17,485)
Restricted stock awards granted
Restricted stock awards granted (in shares)	104,775
Issuance of common stock related to employee stock purchase plan			371			371
Issuance of common stock related to employee stock purchase plan (in shares)	7,890
Tax benefits realized from stock compensation			140			140
Ending balance at Jun. 30, 2016	$ 333	946	507,602	281,071	(1,324)	$ 788,628
Ending balance (in shares) at Jun. 30, 2016	33,584,898					33,584,898
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				54,789		$ 54,789
Other comprehensive income (loss)					1,260	1,260
Stock-based compensation			3,169			3,169
Issuance of common stock related to options exercised, net of shares withheld for payroll taxes	$ 1		256			257
Issuance of common stock related to options exercised, net of shares withheld for payroll taxes (in shares)	60,595
Vesting of restricted stock awards issued at date of grant, net of shares withheld for payroll taxes	$ 1		(2)			(1)
Vesting of restricted stock awards issued at date of grant, net of shares withheld for payroll taxes (in shares)	(16,734)
Restricted stock awards granted
Restricted stock awards granted (in shares)	91,097
Issuance of common stock related to employee stock purchase plan			402			402
Issuance of common stock related to employee stock purchase plan (in shares)	7,527
Vesting of performance based stock awards, net of shares withheld for payroll taxes
Vesting of performance based stock awards, net of shares withheld for payroll taxes (in shares)	3,589
Ending balance at Jun. 30, 2017	$ 340		$ 517,356	$ 386,100	$ (1,121)	$ 902,675
Ending balance (in shares) at Jun. 30, 2017	34,169,924					34,169,924