Consolidated Statements of Shareholders' Equity (unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid in Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]
Beginning balance, value at Dec. 31, 2018	$ 334,753	$ 607	$ 203,680	$ 395,590	$ (265,124)
Beginning balance, shares at Dec. 31, 2018		60,747,000			3,470,000
Vesting of restricted stock		$ 2	(2)
Vesting of restricted stock, shares		280,000
Stock-based compensation	36,187		36,187
Repurchases of common stock	(19,669)				$ (19,669)
Repurchases of common stock, shares					110,000
Net income	47,282			47,282
Ending balance, value at Mar. 31, 2019	398,553	$ 609	239,865	442,872	$ (284,793)
Ending balance, shares at Mar. 31, 2019		61,027,000			3,580,000
Beginning balance, value at Dec. 31, 2019	526,628	$ 613	257,501	576,166	$ (307,652)
Beginning balance, shares at Dec. 31, 2019		61,350,000			3,689,000
Vesting of restricted stock		$ 1	(1)
Vesting of restricted stock, shares		2,000
Stock-based compensation	18,313		18,313
Repurchases of common stock	(8,168)				$ (8,168)
Repurchases of common stock, shares					41,000
Net income	63,015			63,015
Ending balance, value at Mar. 31, 2020	$ 599,788	$ 614	$ 275,813	$ 639,181	$ (315,820)
Ending balance, shares at Mar. 31, 2020		61,352,000			3,730,000