Stockholders Equity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 1,224,503	$ 1,203,056	$ 1,295,586	$ 1,260,321	$ 1,203,056	$ 1,260,321
Comprehensive income	42,314	25,814	(12,491)	69,331	68,128	56,840
Dividends declared	$ (8,086)	$ (8,217)	$ (8,342)	$ (7,453)
Dividends declared (in dollars per share)	$ 0.16	$ 0.16	$ 0.16	$ 0.14
Common stock repurchases	$ (50,347)		$ (84,574)	$ (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	3,001	$ 3,850	2,984	2,633
Balance	1,211,385	1,224,503	1,193,163	1,295,586	1,211,385	1,193,163
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 634	$ 634	$ 631	$ 630	$ 634	$ 630
Balance (in shares)	63,418	63,367	63,054	63,034	63,367	63,034
Employee stock plans			$ 0	$ 1
Employee stock plans (in shares)	18	51	13	20
Balance	$ 634	$ 634	$ 631	$ 631	$ 634	$ 631
Balance (in shares)	63,436	63,418	63,067	63,054	63,436	63,067
Additional Paid-In Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 474,857	$ 470,818	$ 460,239	$ 457,365	$ 470,818	$ 457,365
Employee stock plans	3,285	4,039	3,078	2,874
Balance	478,142	474,857	463,317	460,239	478,142	463,317
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 441,748	$ 441,668	$ 331,607	$ 297,998	$ 441,668	$ 297,998
Balance (in shares)	12,035	12,034	10,190	9,656	12,034	9,656
Common stock repurchases	$ (50,347)		$ (84,574)	$ (33,541)
Common stock repurchases (in shares)	900		1,422	533
Employee stock plans	$ 106	$ 80	$ 107	$ 68
Employee stock plans (in shares)	2	1	2	1
Balance	$ 492,201	$ 441,748	$ 416,288	$ 331,607	$ 492,201	$ 416,288
Balance (in shares)	12,937	12,035	11,614	10,190	12,937	11,614
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 1,389,438	$ 1,363,772	$ 1,261,540	$ 1,206,723	$ 1,363,772	$ 1,206,723
Comprehensive income	37,616	33,992	49,429	38,818
Dividends declared	(8,086)	(8,217)	(8,342)	(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	(178)	(109)	13	(174)
Balance	1,418,790	1,389,438	1,302,640	1,261,540	1,418,790	1,302,640
Accumulated Other Non-Owner Changes to Equity
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(198,678)	(190,500)	(95,217)	(106,399)	(190,500)	(106,399)
Comprehensive income	4,698	(8,178)	(61,920)	30,513
Reclassification pursuant to accounting guidance related to U.S. Tax Reform (Note 3)				(19,331)
Balance	$ (193,980)	$ (198,678)	$ (157,137)	$ (95,217)	$ (193,980)	$ (157,137)

Reclassification Pursuant to Accounting Guidance Related to U.S. Tax Reform

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Aggregate dividends declared during the period for each share of common stock outstanding.

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Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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Amount of paid and unpaid common stock dividends declared with the form of settlement in cash.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Number of shares issued which are neither cancelled nor held in the treasury.

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