Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Total
Beginning balance at Dec. 31, 2019	$ 331	$ 684,354	$ 377,014	$ 1,061,699
Beginning balance, shares at Dec. 31, 2019	33,067
Vesting of restricted stock units	$ 5	(5)
Vesting of restricted stock units, shares	454
Withholding of common stock upon vesting of restricted stock units	$ (2)	(5,143)		(5,145)
Withholding of common stock upon vesting of restricted stock units, shares	(170)
Stock-based compensation expense		8,588		8,588
Other		(230)		(230)
Net income			64,576	64,576
Ending balance at Jun. 30, 2020	$ 334	687,564	441,590	1,129,488
Ending balance, shares at Jun. 30, 2020	33,351
Beginning balance at Mar. 31, 2020	$ 333	681,060	403,140	1,084,533
Beginning balance, shares at Mar. 31, 2020	33,319
Vesting of restricted stock units	$ 1	(1)
Vesting of restricted stock units, shares	42
Withholding of common stock upon vesting of restricted stock units		(168)		(168)
Withholding of common stock upon vesting of restricted stock units, shares	(10)
Stock-based compensation expense		6,903		6,903
Other		(230)		(230)
Net income			38,450	38,450
Ending balance at Jun. 30, 2020	$ 334	687,564	441,590	1,129,488
Ending balance, shares at Jun. 30, 2020	33,351
Beginning balance at Dec. 31, 2020	$ 334	697,200	583,171	1,280,705
Beginning balance, shares at Dec. 31, 2020	33,351
Vesting of restricted stock units	$ 7	(7)
Vesting of restricted stock units, shares	675
Withholding of common stock upon vesting of restricted stock units	$ (3)	(13,723)		(13,726)
Withholding of common stock upon vesting of restricted stock units, shares	(265)
Stock-based compensation expense		7,212		7,212
Cash dividends declared		55	(5,120)	(5,065)
Other		(30)		(30)
Net income			219,562	219,562
Ending balance at Jun. 30, 2021	$ 338	690,707	797,613	1,488,658
Ending balance, shares at Jun. 30, 2021	33,761
Beginning balance at Mar. 31, 2021	$ 337	688,009	684,823	1,373,169
Beginning balance, shares at Mar. 31, 2021	33,708
Vesting of restricted stock units	$ 1	(1)
Vesting of restricted stock units, shares	74
Withholding of common stock upon vesting of restricted stock units		(1,549)		(1,549)
Withholding of common stock upon vesting of restricted stock units, shares	(21)
Stock-based compensation expense		4,193		4,193
Cash dividends declared		55	(5,120)	(5,065)
Net income			117,910	117,910
Ending balance at Jun. 30, 2021	$ 338	$ 690,707	$ 797,613	$ 1,488,658
Ending balance, shares at Jun. 30, 2021	33,761