CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Retained Earnings
Balance (in shares) at Dec. 31, 2015		32,509,000
Balance at Dec. 31, 2015	$ 1,543,780	$ 325	$ 1,440,321	$ (7,594)	$ 110,728
Net income (loss)	85,071				85,071
Other comprehensive loss	(5,445)			(5,445)
Exercise of stock options (in shares)		29,000
Exercise of stock options	3,303	$ 0	3,303
Restricted stock grants (in shares)		195,000
Restricted stock grants	0	$ 2	(2)
Restricted stock grants surrendered (in shares)		(142,000)
Restricted stock grants surrendered	(16,424)	$ (1)	(16,423)
Stock compensation expense, net of forfeitures	36,388		36,388
Employee stock purchase plan (in shares)		15,000
Employee stock purchase plan	2,842	$ 0	2,842
Excess tax benefit from stock-based compensation	4,698		4,698
Balance (in shares) at Dec. 31, 2016		32,606,000
Balance at Dec. 31, 2016	1,654,213	$ 326	1,471,127	(13,039)	195,799
Net income (loss)	122,695				122,695
Other comprehensive loss	4,019			4,019
Exercise of stock options (in shares)		82,000
Exercise of stock options	6,797	$ 1	6,796
Restricted stock grants (in shares)		187,000
Restricted stock grants	0	$ 2
Restricted stock grants adjustments			(2)
Restricted stock grants surrendered (in shares)		(99,000)
Restricted stock grants surrendered	(14,902)	$ (1)	(14,901)
Stock compensation expense, net of forfeitures	38,921		38,921
Stock issued for equity offering (in shares)		3,317,000
Stock issued for equity offering	833,911	$ 33	833,878
Employee stock purchase plan (in shares)		14,000
Employee stock purchase plan	3,434	$ 0	3,434
Balance (in shares) at Dec. 31, 2017		36,107,000
Balance at Dec. 31, 2017	2,651,250	$ 361	2,339,253	(9,020)	320,656
Balance at January 1, 2018	2,705,714	$ 361	2,339,253	(9,020)	375,120
Net income (loss)	238,334				238,334
Other comprehensive loss	(2,668)			(2,668)
Exercise of stock options (in shares)		177,000
Exercise of stock options	21,993	$ 2	21,991
Restricted stock grants (in shares)		160,000
Restricted stock grants	0	$ 1	(1)
Restricted stock grants surrendered (in shares)		(116,000)
Restricted stock grants surrendered	(24,327)	$ (1)	(24,326)
Stock compensation expense, net of forfeitures	40,889		40,889
Employee stock purchase plan (in shares)		15,000
Employee stock purchase plan	5,641	$ 0	5,641
Stock issued for acquisitions (in shares)		103,000
Stock issued for acquisitions	36,366	$ 1	36,365
Balance (in shares) at Dec. 31, 2018		36,446,000
Balance at Dec. 31, 2018	$ 3,021,942	$ 364	$ 2,419,812	$ (11,688)	$ 613,454