Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Additional Paid-in Capital	Retained Earnings (Deficit)	Retained Earnings (Deficit) Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income (Loss)
Balance (in shares) at Dec. 31, 2018			39,506,000
Balance at Dec. 31, 2018	$ 223,590	$ (709)	$ 40	$ 453,193	$ (218,646)	$ (709)	$ (10,997)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	32,637		0	0	32,637		0
Foreign currency translation	214		0	0	0		214
Interest rate swaps, net of the change in taxes	(269)		$ 0	0	0		(269)
Repurchases of common stock, net of retirements (shares)			(155,000)
Repurchases of common stock, net of retirements	(23,097)		$ (1)	0	(23,096)		0
Share-based compensation	3,259		$ 0	3,259	0		0
Issuance of shares under share-based compensation plans (shares)			328,000
Issuance of stock under share-based compensation plans	7,071		$ 1	7,070	0		0
Declaration of cash dividends	(17,819)		$ 0	0	(17,819)		0
Balance (in shares) at Mar. 31, 2019			39,679,000
Balance at Mar. 31, 2019	224,877		$ 40	463,522	(227,633)		(11,052)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in unrealized gains (losses) on interest rate swaps, tax amount	$ 90
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201602Member
Balance (in shares) at Dec. 31, 2018			39,506,000
Balance at Dec. 31, 2018	$ 223,590	(709)	$ 40	453,193	(218,646)	(709)	(10,997)
Balance (in shares) at Jun. 30, 2019			39,898,000
Balance at Jun. 30, 2019	343,169		$ 40	472,390	(118,177)		(11,084)
Balance (in shares) at Dec. 31, 2018			39,506,000
Balance at Dec. 31, 2018	223,590	$ (709)	$ 40	453,193	(218,646)	$ (709)	(10,997)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	243,551
Foreign currency translation	(734)
Interest rate swaps, net of the change in taxes	$ (2,074)
Balance (in shares) at Sep. 30, 2019	40,020,216		40,020,000
Balance at Sep. 30, 2019	$ 405,970		$ 40	480,478	(60,743)		(13,805)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in unrealized gains (losses) on interest rate swaps, tax amount	692
Balance (in shares) at Mar. 31, 2019			39,679,000
Balance at Mar. 31, 2019	224,877		$ 40	463,522	(227,633)		(11,052)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	131,390		0	0	131,390		0
Foreign currency translation	1,208		0	0	0		1,208
Interest rate swaps, net of the change in taxes	(1,240)		0	0	0		(1,240)
Share-based compensation	3,335		$ 0	3,335	0		0
Issuance of shares under share-based compensation plans (shares)			219,000
Issuance of stock under share-based compensation plans	5,533		$ 0	5,533	0		0
Declaration of cash dividends	(21,934)		$ 0	0	(21,934)		0
Balance (in shares) at Jun. 30, 2019			39,898,000
Balance at Jun. 30, 2019	343,169		$ 40	472,390	(118,177)		(11,084)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in unrealized gains (losses) on interest rate swaps, tax amount	413
Net Income	79,525		0	0	79,525		0
Foreign currency translation	(2,156)		0	0	0		(2,156)
Interest rate swaps, net of the change in taxes	(565)		$ 0	0	0		(565)
Repurchases of common stock, net of retirements (shares)			(1,000)
Repurchases of common stock, net of retirements	(92)		$ 0	0	(92)		0
Share-based compensation	3,649		$ 0	3,649	0		0
Issuance of shares under share-based compensation plans (shares)			123,000
Issuance of stock under share-based compensation plans	4,439		$ 0	4,439	0		0
Declaration of cash dividends	$ (21,999)		$ 0	0	(21,999)		0
Balance (in shares) at Sep. 30, 2019	40,020,216		40,020,000
Balance at Sep. 30, 2019	$ 405,970		$ 40	480,478	(60,743)		(13,805)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in unrealized gains (losses) on interest rate swaps, tax amount	$ 188
Balance (in shares) at Dec. 31, 2019	40,074,160		40,074,000
Balance at Dec. 31, 2019	$ 410,180		$ 40	485,239	(64,740)		(10,359)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	30,912		0	0	30,912		0
Foreign currency translation	(5,430)		0	0	0		(5,430)
Interest rate swaps, net of the change in taxes	(8,510)		$ 0	0	0		(8,510)
Repurchases of common stock, net of retirements (shares)			(362,000)
Repurchases of common stock, net of retirements	(66,619)		$ 0	0	(66,619)		0
Share-based compensation	3,654		$ 0	3,654	0		0
Issuance of shares under share-based compensation plans (shares)			219,000
Issuance of stock under share-based compensation plans	6,358		$ 0	6,358	0		0
Declaration of cash dividends	(22,147)		$ 0	0	(22,147)		0
Balance (in shares) at Mar. 31, 2020			39,931,000
Balance at Mar. 31, 2020	348,398		$ 40	495,251	(122,594)		(24,299)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in unrealized gains (losses) on interest rate swaps, tax amount	$ 2,837
Balance (in shares) at Dec. 31, 2019	40,074,160		40,074,000
Balance at Dec. 31, 2019	$ 410,180		$ 40	485,239	(64,740)		(10,359)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	307,565
Foreign currency translation	(320)
Interest rate swaps, net of the change in taxes	$ (10,923)
Balance (in shares) at Sep. 30, 2020	40,153,287		40,153,000
Balance at Sep. 30, 2020	$ 589,501		$ 40	513,030	98,033		(21,602)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in unrealized gains (losses) on interest rate swaps, tax amount	3,641
Balance (in shares) at Mar. 31, 2020			39,931,000
Balance at Mar. 31, 2020	348,398		$ 40	495,251	(122,594)		(24,299)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	157,555		0	0	157,555		0
Foreign currency translation	2,134		0	0	0		2,134
Interest rate swaps, net of the change in taxes	(2,567)		$ 0	0	0		(2,567)
Repurchases of common stock, net of retirements (shares)			(19,000)
Repurchases of common stock, net of retirements	(3,584)		$ 0	0	(3,584)		0
Share-based compensation	3,567		$ 0	3,567	0		0
Issuance of shares under share-based compensation plans (shares)			130,000
Issuance of stock under share-based compensation plans	4,453		$ 0	4,453	0		0
Declaration of cash dividends	(23,165)		$ 0	0	(23,165)		0
Balance (in shares) at Jun. 30, 2020			40,042,000
Balance at Jun. 30, 2020	486,791		$ 40	503,271	8,212		(24,732)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in unrealized gains (losses) on interest rate swaps, tax amount	855
Net Income	119,098
Foreign currency translation	2,976		0	0	0		2,976
Interest rate swaps, net of the change in taxes	154		$ 0	0	0		154
Repurchases of common stock, net of retirements (shares)			(20,000)
Repurchases of common stock, net of retirements	(5,990)		$ 0	0	(5,990)		0
Share-based compensation	3,874		$ 0	3,874	0		0
Issuance of shares under share-based compensation plans (shares)			131,000
Issuance of stock under share-based compensation plans	5,885		$ 0	5,885	0		0
Declaration of cash dividends	$ (23,287)		$ 0	0	(23,287)		0
Balance (in shares) at Sep. 30, 2020	40,153,287		40,153,000
Balance at Sep. 30, 2020	$ 589,501		$ 40	$ 513,030	$ 98,033		$ (21,602)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in unrealized gains (losses) on interest rate swaps, tax amount	$ (51)