Stockholders Equity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 1,203,056	$ 1,260,321
Comprehensive income	25,814	69,331
Dividends declared	$ (8,217)	$ (7,453)
Dividends declared (in dollars per share)	$ 0.16	$ 0.14
Common stock repurchases		$ (33,541)
Reclassification pursuant to accounting guidance related to U.S. Tax Reform (Note 3)		0
Cumulative effect of change in accounting guidance related to Revenue (Note 3)		4,295
Employee stock plans	$ 3,850	2,633
Balance	1,224,503	1,295,586
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 634	$ 630
Balance (in shares)	63,367	63,034
Employee stock plans		$ 1
Employee stock plans (in shares)	51	20
Balance	$ 634	$ 631
Balance (in shares)	63,418	63,054
Additional Paid-In Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 470,818	$ 457,365
Employee stock plans	4,039	2,874
Balance	474,857	460,239
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 441,668	$ 297,998
Balance (in shares)	12,034	9,656
Common stock repurchases		$ (33,541)
Common stock repurchases (in shares)		533
Employee stock plans	$ 80	$ 68
Employee stock plans (in shares)	1	1
Balance	$ 441,748	$ 331,607
Balance (in shares)	12,035	10,190
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 1,363,772	$ 1,206,723
Comprehensive income	33,992	38,818
Dividends declared	(8,217)	(7,453)
Reclassification pursuant to accounting guidance related to U.S. Tax Reform (Note 3)		19,331
Cumulative effect of change in accounting guidance related to Revenue (Note 3)		4,295
Employee stock plans	(109)	(174)
Balance	1,389,438	1,261,540
Accumulated Other Non-Owner Changes to Equity
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(190,500)	(106,399)
Comprehensive income	(8,178)	30,513
Reclassification pursuant to accounting guidance related to U.S. Tax Reform (Note 3)		(19,331)
Balance	$ (198,678)	$ (95,217)