Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Total
Balance (in shares) at Dec. 31, 2015	95,263,461			11,273,746
Balance at Dec. 31, 2015	$ 952	$ 330,290	$ 288,474	$ (95,014)	$ 524,702
Net income			37,636		37,636
Stock-based compensation expense		13,277			13,277
Total Number of Shares Purchased (in shares)				1,140,332
Purchase of treasury stock				$ (20,470)	$ (20,470)
Exercise of stock options (in shares)	510,512				510,512
Exercise of stock options	$ 5	2,935			$ 2,940
Vesting of restricted stock awards and units, net of shares withheld for employee tax (in shares)	192,879
Vesting of restricted stock awards and units, net of shares withheld for employee tax	$ 2	(1,477)			(1,475)
Balance (in shares) at Dec. 31, 2016	95,966,852			12,414,078
Balance at Dec. 31, 2016	$ 959	345,025	326,110	$ (115,484)	556,610
Net income			40,054		40,054
Stock-based compensation expense		24,143			24,143
Total Number of Shares Purchased (in shares)				865,315
Purchase of treasury stock				$ (14,137)	$ (14,137)
Exercise of stock options (in shares)	172,326				172,326
Exercise of stock options	$ 2	2,718			$ 2,720
Vesting of restricted stock awards and units, net of shares withheld for employee tax (in shares)	397,073
Vesting of restricted stock awards and units, net of shares withheld for employee tax	$ 4	(3,165)			(3,161)
Balance (in shares) at Dec. 31, 2017	96,536,251			13,279,393
Balance at Dec. 31, 2017	$ 965	368,721	366,164	$ (129,621)	606,229
Net income			54,989		54,989
Stock-based compensation expense		21,507			$ 21,507
Total Number of Shares Purchased (in shares)				383,801	383,801
Purchase of treasury stock				$ (5,955)	$ (5,955)
Exercise of stock options (in shares)	2,017,442				2,017,442
Exercise of stock options	$ 20	38,342			$ 38,362
Vesting of restricted stock awards and units, net of shares withheld for employee tax (in shares)	370,808
Vesting of restricted stock awards and units, net of shares withheld for employee tax	$ 4	(2,822)			(2,818)
Adoption of accounting standard (Note 1 and 2) (Accounting Standards Update 2014-09 [Member]) at Dec. 31, 2017			1,082		1,082
Balance (in shares) at Dec. 31, 2018	98,924,501			13,663,194
Balance at Dec. 31, 2018	$ 989	$ 425,748	$ 422,235	$ (135,576)	$ 713,396