Stockholders Equity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 1,257,706	$ 1,244,960	$ 1,270,528	$ 1,211,385	$ 1,224,503	$ 1,203,056	$ 1,270,528	$ 1,203,056
Comprehensive income	57,497	17,611	(4,456)	8,424	42,314	25,814	70,652	76,552
Dividends declared	(8,097)	(8,072)	(8,133)	(8,111)	(8,086)	(8,217)
Common stock repurchases			(15,550)		(50,347)
Employee stock plans	550	3,207	2,571	(1,000)	3,001	3,850
Balance	$ 1,307,656	$ 1,257,706	$ 1,244,960	$ 1,210,698	$ 1,211,385	$ 1,224,503	1,307,656	1,210,698
Dividends declared (in dollars per share)	$ 0.16	$ 0.16	$ 0.16	$ 0.16	$ 0.16	$ 0.16
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 639	$ 639	$ 639	$ 634	$ 634	$ 634	$ 639	$ 634
Balance (in shares)	63,904	63,890	63,873	63,436	63,418	63,367	63,873	63,367
Employee stock plans				$ 4	$ 0	$ 0
Employee stock plans (in shares)	237	14	17	321	18	51
Balance	$ 641	$ 639	$ 639	$ 638	$ 634	$ 634	$ 641	$ 638
Balance (in shares)	64,141	63,904	63,890	63,757	63,436	63,418	64,141	63,757
Additional Paid-In Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 495,419	$ 492,025	$ 489,282	$ 478,142	$ 474,857	$ 470,818	$ 489,282	$ 470,818
Employee stock plans	3,601	3,394	2,743	4,713	3,285	4,039
Balance	499,020	495,419	492,025	482,855	478,142	474,857	499,020	482,855
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ (513,761)	$ (513,708)	$ (498,074)	$ (492,201)	$ (441,748)	$ (441,668)	$ (498,074)	$ (441,668)
Balance (in shares)	13,450	13,449	13,051	12,937	12,035	12,034	13,051	12,034
Common stock repurchases			$ (15,550)		$ (50,347)
Common stock repurchases (in shares)			396		900
Employee stock plans	$ (3,039)	$ (53)	$ (84)	$ (5,727)	$ (106)	$ (80)
Employee stock plans (in shares)	76	1	2	112	2	1
Balance	$ (516,800)	$ (513,761)	$ (513,708)	$ (497,928)	$ (492,201)	$ (441,748)	$ (516,800)	$ (497,928)
Balance (in shares)	13,526	13,450	13,449	13,049	12,937	12,035	13,526	13,049
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 1,503,049	$ 1,510,688	$ 1,489,176	$ 1,418,790	$ 1,389,438	$ 1,363,772	$ 1,489,176	$ 1,363,772
Comprehensive income	15,358	567	29,733	45,769	37,616	33,992
Dividends declared	(8,097)	(8,072)	(8,133)	(8,111)	(8,086)	(8,217)
Employee stock plans	(14)	(134)	(88)	10	(178)	(109)
Balance	1,510,296	1,503,049	1,510,688	1,456,458	1,418,790	1,389,438	1,510,296	1,456,458
Accumulated Other Non-Owner Changes to Equity
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(227,640)	(244,684)	(210,495)	(193,980)	(198,678)	(190,500)	(210,495)	(190,500)
Comprehensive income	42,139	17,044	(34,189)	(37,345)	4,698	(8,178)
Balance	$ (185,501)	$ (227,640)	$ (244,684)	$ (231,325)	$ (193,980)	$ (198,678)	$ (185,501)	$ (231,325)