Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital	Retained Earnings (Deficit)	Accumulated Other Comprehensive Income (Loss)
Balance (in shares) at Dec. 31, 2019		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		40,074,000
Balance at Dec. 31, 2019	410,180	$ 40	485,239	(64,740)	(10,359)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	188,467
Foreign currency translation	(3,296)
Interest rate swaps, net of the change in taxes	$ (11,077)
Balance (in shares) at Jun. 30, 2020	40,041,683	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	3,692
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	40,041,683	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
Balance (in shares) at Dec. 31, 2020	40,232,210	40,232,000
Balance at Dec. 31, 2020	$ 639,470	$ 40	519,579	133,870	(14,019)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	98,655	0	0	98,655	0
Foreign currency translation	(1,268)	0	0	0	(1,268)
Interest rate swaps, net of the change in taxes	9,137	$ 0	0	0	9,137
Repurchases of common stock, net of retirements (shares)		(215,000)
Repurchases of common stock, net of retirements	(71,516)	$ 0	0	(71,516)	0
Share-based compensation	3,837	$ 0	3,837	0	0
Issuance of shares under share-based compensation plans (shares)		69,000
Issuance of stock under share-based compensation plans	2,912	$ 0	2,912	0	0
Declaration of cash dividends	(23,299)	$ 0	0	(23,299)	0
Balance (in shares) at Mar. 31, 2021		40,086,000
Balance at Mar. 31, 2021	657,928	$ 40	526,328	137,710	(6,150)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in unrealized gains (losses) on interest rate swaps, tax amount	$ (3,046)
Balance (in shares) at Dec. 31, 2020	40,232,210	40,232,000
Balance at Dec. 31, 2020	$ 639,470	$ 40	519,579	133,870	(14,019)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	358,350
Foreign currency translation	34
Interest rate swaps, net of the change in taxes	$ 6,980
Balance (in shares) at Jun. 30, 2021	40,131,570	40,131,000
Balance at Jun. 30, 2021	$ 874,748	$ 40	535,046	346,667	(7,005)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in unrealized gains (losses) on interest rate swaps, tax amount	(2,327)
Balance (in shares) at Mar. 31, 2021		40,086,000
Balance at Mar. 31, 2021	657,928	$ 40	526,328	137,710	(6,150)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	259,695	0	0	259,695	0
Foreign currency translation	1,302	0	0	0	1,302
Interest rate swaps, net of the change in taxes	(2,157)	$ 0	0	0	(2,157)
Repurchases of common stock, net of retirements (shares)		(45,000)
Repurchases of common stock, net of retirements	(18,619)	$ 0	0	(18,619)	0
Share-based compensation	3,712	$ 0	3,712	0	0
Issuance of shares under share-based compensation plans (shares)		90,000
Issuance of stock under share-based compensation plans	5,006	$ 0	5,006	0	0
Declaration of cash dividends	$ (32,119)	$ 0	0	(32,119)	0
Balance (in shares) at Jun. 30, 2021	40,131,570	40,131,000
Balance at Jun. 30, 2021	$ 874,748	$ 40	$ 535,046	$ 346,667	$ (7,005)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in unrealized gains (losses) on interest rate swaps, tax amount	$ 719