Stockholders Equity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 1,244,960	$ 1,270,528	$ 1,224,503	$ 1,203,056	$ 1,270,528	$ 1,203,056
Comprehensive income	17,611	(4,456)	42,314	25,814	13,155	68,128
Dividends declared	(8,072)	(8,133)	(8,086)	(8,217)
Common stock repurchases		(15,550)	(50,347)
Employee stock plans	3,207	2,571	3,001	3,850
Balance	$ 1,257,706	$ 1,244,960	$ 1,211,385	$ 1,224,503	1,257,706	1,211,385
Dividends declared (in dollars per share)	$ 0.16	$ 0.16	$ 0.16	$ 0.16
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 639	$ 639	$ 634	$ 634	$ 639	$ 634
Balance (in shares)	63,890	63,873	63,418	63,367	63,873	63,367
Employee stock plans			$ 0	$ 0
Employee stock plans (in shares)	14	17	18	51
Balance	$ 639	$ 639	$ 634	$ 634	$ 639	$ 634
Balance (in shares)	63,904	63,890	63,436	63,418	63,904	63,436
Additional Paid-In Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 492,025	$ 489,282	$ 474,857	$ 470,818	$ 489,282	$ 470,818
Employee stock plans	3,394	2,743	3,285	4,039
Balance	495,419	492,025	478,142	474,857	495,419	478,142
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ (513,708)	$ (498,074)	$ (441,748)	$ (441,668)	$ (498,074)	$ (441,668)
Balance (in shares)	13,449	13,051	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	$ (53)	$ (84)	$ (106)	$ (80)
Employee stock plans (in shares)	1	2	2	1
Balance	$ (513,761)	$ (513,708)	$ (492,201)	$ (441,748)	$ (513,761)	$ (492,201)
Balance (in shares)	13,450	13,449	12,937	12,035	13,450	12,937
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 1,510,688	$ 1,489,176	$ 1,389,438	$ 1,363,772	$ 1,489,176	$ 1,363,772
Comprehensive income	567	29,733	37,616	33,992
Dividends declared	(8,072)	(8,133)	(8,086)	(8,217)
Employee stock plans	(134)	(88)	(178)	(109)
Balance	1,503,049	1,510,688	1,418,790	1,389,438	1,503,049	1,418,790
Accumulated Other Non-Owner Changes to Equity
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(244,684)	(210,495)	(198,678)	(190,500)	(210,495)	(190,500)
Comprehensive income	17,044	(34,189)	4,698	(8,178)
Balance	$ (227,640)	$ (244,684)	$ (193,980)	$ (198,678)	$ (227,640)	$ (193,980)