Stockholders Equity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ (1,211,385)	$ (1,224,503)	$ (1,203,056)	$ (1,193,163)	$ (1,295,586)	$ (1,260,321)	$ (1,203,056)	$ (1,260,321)
Comprehensive income	8,424	42,314	25,814	44,114	(12,491)	69,331	76,552	100,955
Dividends declared	$ (8,111)	$ (8,086)	$ (8,217)	$ (8,201)	$ (8,342)	$ (7,453)
Dividends declared (in dollars per share)	$ 0.16	$ 0.16	$ 0.16	$ 0.16	$ 0.16	$ 0.14
Common stock repurchases		$ (50,347)		$ (20,160)	$ (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	$ 1,000	(3,001)	$ (3,850)	2,011	(2,984)	(2,633)
Balance	(1,210,698)	(1,211,385)	(1,224,503)	(1,206,905)	(1,193,163)	(1,295,586)	(1,210,698)	(1,206,905)
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ (634)	$ (634)	$ (634)	$ (631)	$ (631)	$ (630)	$ (634)	$ (630)
Balance (in shares)	63,436	63,418	63,367	63,067	63,054	63,034	63,367	63,034
Employee stock plans				$ (2)	$ 0	$ (1)
Employee stock plans (in shares)	321	18	51	226	13	20
Balance	$ (638)	$ (634)	$ (634)	$ (633)	$ (631)	$ (631)	$ (638)	$ (633)
Balance (in shares)	63,757	63,436	63,418	63,293	63,067	63,054	63,757	63,293
Additional Paid-In Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ (478,142)	$ (474,857)	$ (470,818)	$ (463,317)	$ (460,239)	$ (457,365)	$ (470,818)	$ (457,365)
Employee stock plans	(4,713)	(3,285)	(4,039)	(3,293)	(3,078)	(2,874)
Balance	(482,855)	(478,142)	(474,857)	(466,610)	(463,317)	(460,239)	(482,855)	(466,610)
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ (492,201)	$ (441,748)	$ (441,668)	$ (416,288)	$ (331,607)	$ (297,998)	$ (441,668)	$ (297,998)
Balance (in shares)	12,937	12,035	12,034	11,614	10,190	9,656	12,034	9,656
Common stock repurchases		$ (50,347)		$ (20,160)	$ (84,574)	$ (33,541)
Common stock repurchases (in shares)		900		337	1,422	533
Employee stock plans	$ (5,727)	$ (106)	$ (80)	$ (4,974)	$ (107)	$ (68)
Employee stock plans (in shares)	112	2	1	79	2	1
Balance	$ (497,928)	$ (492,201)	$ (441,748)	$ (441,422)	$ (416,288)	$ (331,607)	$ (497,928)	$ (441,422)
Balance (in shares)	13,049	12,937	12,035	12,030	11,614	10,190	13,049	12,030
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ (1,418,790)	$ (1,389,438)	$ (1,363,772)	$ (1,302,640)	$ (1,261,540)	$ (1,206,723)	$ (1,363,772)	$ (1,206,723)
Comprehensive income	45,769	37,616	33,992	39,109	49,429	38,818
Dividends declared	(8,111)	(8,086)	(8,217)	(8,201)	(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	(10)	178	109	332	(13)	174
Balance	(1,456,458)	(1,418,790)	(1,389,438)	(1,333,216)	(1,302,640)	(1,261,540)	(1,456,458)	(1,333,216)
Accumulated Other Non-Owner Changes to Equity
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	193,980	198,678	190,500	157,137	95,217	106,399	190,500	106,399
Comprehensive income	(37,345)	4,698	(8,178)	5,005	(61,920)	30,513
Reclassification pursuant to accounting guidance related to U.S. Tax Reform (Note 3)						(19,331)
Balance	$ 231,325	$ 193,980	$ 198,678	$ 152,132	$ 157,137	$ 95,217	$ 231,325	$ 152,132