UNAUDITED CONDENSED CONSOLIDATED STATEMENT OF CHANGES IN STOCKHOLDERS’ 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
Shares at beginning of period (in shares) at Dec. 31, 2019			72,202					49,277
Beginning of period at Dec. 31, 2019	$ 167,263	$ (214)	$ 722	$ 459,545	$ (1,526)	$ 350,545	$ (214)	$ (642,023)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	9,106					9,106
Issuance for stock-based compensation and dividends, net of forfeitures (in shares)			4
Issuance for stock-based compensation and dividends, net of forfeitures	0			218		(218)
Stock-based compensation expense	2,896			2,896
Employee stock purchase plan (in shares)								(4)
Employee stock purchase plan	142			93				$ 49
Dividends	(4,293)					(4,293)
Change in fair value of interest rate swaps	(1,121)				(1,121)
Repurchases of common stock (in shares)								685
Repurchases of common stock	(20,380)							$ (20,380)
Shares at end of period (in shares) at Mar. 31, 2020			72,198					49,958
End of period at Mar. 31, 2020	153,399		$ 722	462,752	(2,647)	354,926		$ (662,354)
Shares at beginning of period (in shares) at Dec. 31, 2019			72,202					49,277
Beginning of period at Dec. 31, 2019	167,263	$ (214)	$ 722	459,545	(1,526)	350,545	$ (214)	$ (642,023)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	37,754
Employee stock purchase plan	411
Defined benefit pension plans	0
Change in fair value of interest rate swaps	(1,473)
Shares at end of period (in shares) at Sep. 30, 2020			72,247					50,291
End of period at Sep. 30, 2020	170,206		$ 722	469,177	(2,999)	374,767		$ (671,461)
Shares at beginning of period (in shares) at Mar. 31, 2020			72,198					49,958
Beginning of period at Mar. 31, 2020	153,399		$ 722	462,752	(2,647)	354,926		$ (662,354)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	9,885					9,885
Issuance for stock-based compensation and dividends, net of forfeitures (in shares)			39
Issuance for stock-based compensation and dividends, net of forfeitures	0			240		(240)
Stock-based compensation expense	2,903			2,903
Employee stock purchase plan (in shares)								(5)
Employee stock purchase plan	134			62				$ 72
Dividends	(4,162)					(4,162)
Change in fair value of interest rate swaps	(470)				(470)
Repurchases of common stock (in shares)								342
Repurchases of common stock	(9,213)							$ (9,213)
Shares at end of period (in shares) at Jun. 30, 2020			72,237					50,295
End of period at Jun. 30, 2020	152,476		$ 722	465,957	(3,117)	360,409		$ (671,495)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	18,763					18,763
Issuance for stock-based compensation and dividends, net of forfeitures (in shares)			10
Issuance for stock-based compensation and dividends, net of forfeitures	0			241		(241)
Stock-based compensation expense	2,908			2,908
Employee stock purchase plan (in shares)								(5)
Employee stock purchase plan	135			71				$ 64
Dividends	(4,164)					(4,164)
Defined benefit pension plans	0
Change in fair value of interest rate swaps	118				118
Repurchases of common stock (in shares)								1
Repurchases of common stock	(30)							$ (30)
Shares at end of period (in shares) at Sep. 30, 2020			72,247					50,291
End of period at Sep. 30, 2020	170,206		$ 722	469,177	(2,999)	374,767		$ (671,461)
Shares at beginning of period (in shares) at Dec. 31, 2020			72,600					50,427
Beginning of period at Dec. 31, 2020	179,935		$ 726	472,378	(4,423)	388,645		$ (677,391)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	13,261					13,261
Issuance for stock-based compensation and dividends, net of forfeitures (in shares)			15
Issuance for stock-based compensation and dividends, net of forfeitures	0			271		(271)
Stock-based compensation expense	3,403			3,403
Employee stock purchase plan (in shares)								(4)
Employee stock purchase plan	170			113				$ 57
Dividends	(4,786)					(4,786)
Defined benefit pension plans	47				47
Change in fair value of interest rate swaps	939				939
Repurchases of common stock (in shares)								317
Repurchases of common stock	(16,313)							$ (16,313)
Shares at end of period (in shares) at Mar. 31, 2021			72,615					50,740
End of period at Mar. 31, 2021	176,656		$ 726	476,165	(3,437)	396,849		$ (693,647)
Shares at beginning of period (in shares) at Dec. 31, 2020			72,600					50,427
Beginning of period at Dec. 31, 2020	179,935		$ 726	472,378	(4,423)	388,645		$ (677,391)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	54,617
Employee stock purchase plan	558
Defined benefit pension plans	3,103
Change in fair value of interest rate swaps	1,101
Shares at end of period (in shares) at Sep. 30, 2021			72,640					51,207
End of period at Sep. 30, 2021	189,969		$ 726	484,034	(219)	427,622		$ (722,194)
Shares at beginning of period (in shares) at Mar. 31, 2021			72,615					50,740
Beginning of period at Mar. 31, 2021	176,656		$ 726	476,165	(3,437)	396,849		$ (693,647)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	21,188					21,188
Issuance for stock-based compensation and dividends, net of forfeitures (in shares)			40
Issuance for stock-based compensation and dividends, net of forfeitures	2		$ 1	274		(273)
Stock-based compensation expense	3,532			3,532
Employee stock purchase plan (in shares)								(4)
Employee stock purchase plan	195			143				$ 52
Dividends	(4,746)					(4,746)
Defined benefit pension plans	3,056				3,056
Change in fair value of interest rate swaps	10				10
Repurchases of common stock (in shares)								225
Repurchases of common stock	(13,614)							$ (13,614)
Shares at end of period (in shares) at Jun. 30, 2021			72,655					50,961
End of period at Jun. 30, 2021	186,279		$ 727	480,114	(371)	413,018		$ (707,209)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	20,168					20,168
Issuance for stock-based compensation and dividends, net of forfeitures (in shares)			(15)
Issuance for stock-based compensation and dividends, net of forfeitures	(1)			260		(260)
Stock-based compensation expense	3,512			3,512
Employee stock purchase plan (in shares)								(3)
Employee stock purchase plan	193			148				$ 45
Dividends	(5,304)					(5,304)
Defined benefit pension plans	0
Change in fair value of interest rate swaps	152				152
Repurchases of common stock (in shares)								249
Repurchases of common stock	(15,030)							$ (15,030)
Shares at end of period (in shares) at Sep. 30, 2021			72,640					51,207
End of period at Sep. 30, 2021	$ 189,969		$ 726	$ 484,034	$ (219)	$ 427,622		$ (722,194)