CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Treasury Stock
Balance at Dec. 31, 2018	$ 1,324,846	$ (1,116)	$ 481	$ 731,435	$ (46)	$ 771,925	$ (1,116)	$ (178,949)
Beginning balance (in shares) at Dec. 31, 2018			48,148					(9,872)
Increase (Decrease) in Stockholders' Equity
Net income	27,348					27,348
Exercise of stock options and vesting of restricted stock units	$ 6,528			(14,405)				$ 20,933
Exercise of stock options and vesting of restricted stock units (in shares)	94							111
Employee taxes paid for withheld shares upon equity award settlement	$ (1,337)							$ (1,337)
Employee taxes paid for withheld shares upon equity award settlement (in shares)								(7)
Stock compensation	14,416			14,416
Issuance of shares pursuant to employee stock purchase plan	$ 2,349			(373)				$ 2,722
Issuance of shares pursuant to employee stock purchase plan (in shares)	15							15
Treasury stock purchases	$ (14,289)							$ (14,289)
Treasury stock purchases (in shares)	(72)							(72)
Balance at Mar. 31, 2019	$ 1,358,745		$ 481	731,073	(46)	798,157		$ (170,920)
Ending balance (in shares) at Mar. 31, 2019			48,148					(9,825)
Balance at Dec. 31, 2019	1,617,058		$ 481	739,478	(46)	917,336		$ (40,191)
Beginning balance (in shares) at Dec. 31, 2019			48,148					(8,839)
Increase (Decrease) in Stockholders' Equity
Net income	47,550
Exercise of stock options and vesting of restricted stock units	$ 46,236			38,942				$ 7,294
Exercise of stock options and vesting of restricted stock units (in shares)	481							498
Employee taxes paid for withheld shares upon equity award settlement	$ (2,301)							$ (2,301)
Employee taxes paid for withheld shares upon equity award settlement (in shares)								(7)
Stock compensation	17,302			17,302
Issuance of shares pursuant to employee stock purchase plan	$ 2,469			2,367				$ 102
Issuance of shares pursuant to employee stock purchase plan (in shares)	10							10
Treasury stock purchases	$ (15,482)							$ (15,482)
Treasury stock purchases (in shares)	(59)							(59)
Balance at Mar. 31, 2020	$ 1,712,832		$ 481	$ 798,089	$ (46)	$ 964,886		$ (50,578)
Ending balance (in shares) at Mar. 31, 2020			48,148					(8,397)