Consolidated Statements of Stockholders' Equity Statement - USD ($) $ in Thousands	Total	Common Stock	Additional paid-in capital	Accumulated other comprehensive (loss) income	Retained earnings
Balance (in shares) at Dec. 31, 2018		39,386,000
Balance at Dec. 31, 2018	$ 425,584	$ 39	$ 363,921	$ (139)	$ 61,763
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under equity compensation plans (in shares)		444,000
Issuance of common stock under equity compensation plans	8,817	$ 1	8,816
Stock-based compensation expense	2,887		2,887
Repurchases of common stock (in shares)		(24,000)
Repurchases of common stock	(1,476)		(1,476)
Other comprehensive gain, net of tax				42
Net income	24,844				24,844
Balance (in shares) at Mar. 31, 2019		39,806,000
Balance at Mar. 31, 2019	460,698	$ 40	374,148	(97)	86,607
Balance (in shares) at Dec. 31, 2018		39,386,000
Balance at Dec. 31, 2018	425,584	$ 39	363,921	(139)	61,763
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive gain, net of tax	(698)
Net income	42,295
Balance (in shares) at Sep. 30, 2019		41,642,000
Balance at Sep. 30, 2019	534,163	$ 42	429,920	143	104,058
Balance (in shares) at Mar. 31, 2019		39,806,000
Balance at Mar. 31, 2019	460,698	$ 40	374,148	(97)	86,607
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under equity compensation plans (in shares)		122,000
Issuance of common stock under equity compensation plans	1,433		1,433
Stock-based compensation expense	3,309		3,309
Derivative liabilities - Convertible Senior Notes elected to settle in cash	(590)		(590)
Repurchases of common stock (in shares)		(7,000)
Repurchases of common stock	(395)		(395)
Net income	1,270				1,270
Balance (in shares) at Jun. 30, 2019		41,418,000
Balance at Jun. 30, 2019	509,963	$ 41	421,996	49	87,877
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments	(43,516)		(43,516)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	146			146
Stock Issued During Period, Value, Conversion of Convertible Securities	86,428	$ 1	86,427
Debt Conversion, Converted Instrument, Shares Issued		1,497,000
Issuance of common stock under equity compensation plans (in shares)		225,000
Issuance of common stock under equity compensation plans	4,924	$ 1	4,923
Stock-based compensation expense	3,030		3,030
Repurchases of common stock (in shares)		(1,000)
Repurchases of common stock	(29)		(29)
Other comprehensive gain, net of tax	(544)
Net income	16,181				16,181
Balance (in shares) at Sep. 30, 2019		41,642,000
Balance at Sep. 30, 2019	534,163	$ 42	429,920	143	104,058
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	94			94
Balance (in shares) at Dec. 31, 2019		41,868,000
Balance at Dec. 31, 2019	559,820	$ 42	425,557	(463)	134,684
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under equity compensation plans (in shares)		153,000
Issuance of common stock under equity compensation plans	3,571	$ 0	3,571
Stock-based compensation expense	3,325		3,325
Repurchases of common stock (in shares)		(25,000)
Repurchases of common stock	(1,954)		(1,954)
Other comprehensive gain, net of tax				200
Net income	40,237				40,237
Balance (in shares) at Mar. 31, 2020		41,996,000
Balance at Mar. 31, 2020	605,199	$ 42	430,499	(263)	174,921
Balance (in shares) at Dec. 31, 2019		41,868,000
Balance at Dec. 31, 2019	$ 559,820	$ 42	425,557	(463)	134,684
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchases of common stock (in shares)	(257,329)
Repurchases of common stock		$ (43,700)
Other comprehensive gain, net of tax	$ 1,037
Net income	340,157
Balance (in shares) at Sep. 30, 2020		42,037,000
Balance at Sep. 30, 2020	849,247	$ 42	375,255	(891)	474,841
Balance (in shares) at Mar. 31, 2020		41,996,000
Balance at Mar. 31, 2020	605,199	$ 42	430,499	(263)	174,921
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under equity compensation plans (in shares)		203,000
Issuance of common stock under equity compensation plans	3,287	$ 0	3,287
Stock-based compensation expense	4,665		4,665
Derivative liabilities - Convertible Senior Notes elected to settle in cash	(26,180)		(26,180)
Repurchases of common stock (in shares)		(252,000)
Repurchases of common stock	(42,894)		(42,894)
Net income	67,652				67,652
Balance (in shares) at Jun. 30, 2020		41,949,000
Balance at Jun. 30, 2020	611,709	$ 42	369,425	(331)	242,573
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent				(68)
Stock Issued During Period, Value, Conversion of Convertible Securities	48	$ 0	48
Debt Conversion, Converted Instrument, Shares Issued		2,000
Issuance of common stock under equity compensation plans (in shares)		88,000
Issuance of common stock under equity compensation plans	2,733		2,733
Stock-based compensation expense	$ 5,021		5,021
Repurchases of common stock (in shares)	(10,157)	(14,000)
Repurchases of common stock	$ (2,384)	$ (1,500)	(2,384)
Other comprehensive gain, net of tax	837
Net income	232,268				232,268
Balance (in shares) at Sep. 30, 2020		42,037,000
Balance at Sep. 30, 2020	849,247	$ 42	375,255	(891)	$ 474,841
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(560)			$ (560)
Stock Issued During Period, Value, Conversion of Convertible Securities	$ 460	$ 0	$ 460
Debt Conversion, Converted Instrument, Shares Issued		14,000