CONDENSED CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Balance at Dec. 31, 2019	$ 726,283	$ 360	$ (6,030)	$ 666,585	$ 68,109	$ (2,741)
Net income	28,954				28,954
Foreign currency translation	(988)					(988)
Stock-based compensation expense	5,445			5,445
Stock options exercised	1,343	1		1,342
Repurchases of common stock	(43,238)	(6)			(43,232)
Balance at Mar. 31, 2020	717,799	355	(6,030)	673,372	53,831	(3,729)
Balance at Dec. 31, 2019	726,283	360	(6,030)	666,585	68,109	(2,741)
Net income	53,058
Foreign currency translation	(482)
Balance at Jun. 30, 2020	738,069	354	(6,030)	676,621	70,347	(3,223)
Balance at Mar. 31, 2020	717,799	355	(6,030)	673,372	53,831	(3,729)
Net income	24,104				24,104
Foreign currency translation	506					506
Stock-based compensation expense	2,616			2,616
Stock options exercised	633			633
Repurchases of common stock	(7,589)	(1)	0	0	(7,588)	0
Balance at Jun. 30, 2020	738,069	354	(6,030)	676,621	70,347	(3,223)
Balance at Dec. 31, 2020	805,779	355	(5,578)	695,904	115,229	(131)
Net income	43,306				43,306
Foreign currency translation	(2,135)					(2,135)
Stock-based compensation expense	2,871			2,871
Stock options exercised	9,106	4		9,102
Balance at Mar. 31, 2021	858,927	359	(5,578)	707,877	158,535	(2,266)
Balance at Dec. 31, 2020	805,779	355	(5,578)	695,904	115,229	(131)
Net income	83,240
Foreign currency translation	(1,629)
Balance at Jun. 30, 2021	851,882	358	(5,578)	716,547	142,315	(1,760)
Balance at Mar. 31, 2021	858,927	359	(5,578)	707,877	158,535	(2,266)
Net income	39,934				39,934
Foreign currency translation	506					506
Stock-based compensation expense	3,570			3,570
Stock options exercised	5,102	2		5,100
Repurchases of common stock	(56,157)	(3)			(56,154)
Balance at Jun. 30, 2021	$ 851,882	$ 358	$ (5,578)	$ 716,547	$ 142,315	$ (1,760)