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, 2017	$ 1,191,736		$ 481	$ 626,867	$ (46)	$ 624,463		$ (60,029)
Balance, shares at Dec. 31, 2017			48,148					10,262
Increase (Decrease) in Stockholders' Equity
Net income	147,462					147,462
Issuance/ Exercise of stock options	$ 74,907			44,458				$ 30,449
Issuance/ Exercise of stock options (in shares)	1,126							1,126
Stock compensation	$ 52,740			52,740
Issuance of shares pursuant to employee stock purchase plan	$ 8,051			7,370				$ 681
Issuance of shares pursuant to employee stock purchase plan (in shares)	45							45
Treasury stock purchases	$ (150,050)							$ (150,050)
Treasury stock purchases (in shares)	(781)							(781)
Balance at Dec. 31, 2018	$ 1,324,846	$ (1,116)	$ 481	731,435	(46)	771,925	$ (1,116)	$ (178,949)
Balance, shares at Dec. 31, 2018			48,148					9,872
Increase (Decrease) in Stockholders' Equity
Accounting Standards Update	us-gaap:AccountingStandardsUpdate201602Member
Net income	$ 146,527					146,527
Issuance/ Exercise of stock options	$ 96,908			(52,833)				$ 149,741
Issuance/ Exercise of stock options (in shares)	999							1,075
Employee taxes paid for withheld shares for taxes upon equity award settlement	$ (5,361)							$ (5,361)
Employee taxes paid for withheld shares for taxes upon equity award settlement (in shares)								(23)
Stock compensation	59,967			59,967
Issuance of shares pursuant to employee stock purchase plan	$ 9,576			909				$ 8,667
Issuance of shares pursuant to employee stock purchase plan (in shares)	53							53
Treasury stock purchases	$ (14,289)							$ (14,289)
Treasury stock purchases (in shares)	(72)							(72)
Balance at Dec. 31, 2019	$ 1,617,058		$ 481	739,478	(46)	917,336		$ (40,191)
Balance, shares at Dec. 31, 2019			48,148					8,839
Increase (Decrease) in Stockholders' Equity
Net income	194,820					194,820
Issuance/ Exercise of stock options	$ 124,363			90,636				$ 33,727
Issuance/ Exercise of stock options (in shares)	1,174							1,283
Employee taxes paid for withheld shares for taxes upon equity award settlement	$ (12,923)							$ (12,923)
Employee taxes paid for withheld shares for taxes upon equity award settlement (in shares)								(34)
Stock compensation	67,365			67,365
Issuance of shares pursuant to employee stock purchase plan	$ 10,912			7,853				$ 3,059
Issuance of shares pursuant to employee stock purchase plan (in shares)	40							40
Treasury stock purchases	$ (15,484)							$ (15,484)
Treasury stock purchases (in shares)	(59)							(59)
Balance at Dec. 31, 2020	$ 1,986,111		$ 481	$ 905,332	$ (46)	$ 1,112,156		$ (31,812)
Balance, shares at Dec. 31, 2020			48,148					7,609