Stockholders Equity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	$ 1,390,393	$ 1,351,367	$ 1,382,677	$ 1,257,706	$ 1,244,960	$ 1,270,528	$ 1,382,677	$ 1,270,528
Comprehensive income	6,182	49,082	(25,520)	57,497	17,611	(4,456)	29,744	70,652
Dividends declared	(8,099)	(8,090)	(8,104)	(8,097)	(8,072)	(8,133)
Common stock repurchases		(5,229)				(15,550)
Residual interest in subsidiary	2,177
Employee stock plans	2,576	3,263	2,314	550	3,207	2,571
Balance at end of period	$ 1,393,229	$ 1,390,393	$ 1,351,367	$ 1,307,656	$ 1,257,706	$ 1,244,960	$ 1,393,229	$ 1,307,656
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 at beginning of period (in shares)	64,200	64,183	64,171	63,904	63,890	63,873	64,171	63,873
Balance at beginning of period	$ 642	$ 642	$ 642	$ 639	$ 639	$ 639	$ 642	$ 639
Employee stock plans (in shares)	84	17	12	237	14	17
Employee stock plans	$ 1			$ 2	$ 0	$ 0
Balance at end of period (in shares)	64,284	64,200	64,183	64,141	63,904	63,890	64,284	64,141
Balance at end of period	$ 643	$ 642	$ 642	$ 641	$ 639	$ 639	$ 643	$ 641
Additional Paid-In Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	507,354	503,937	501,531	495,419	492,025	489,282	501,531	489,282
Residual interest in subsidiary	2,177
Employee stock plans	3,826	3,417	2,406	3,601	3,394	2,743
Balance at end of period	$ 513,357	$ 507,354	$ 503,937	$ 499,020	$ 495,419	$ 492,025	$ 513,357	$ 499,020
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period (in shares)	13,634	13,531	13,530	13,450	13,449	13,051	13,530	13,051
Balance at beginning of period	$ (522,412)	$ (517,060)	$ (516,992)	$ (513,761)	$ (513,708)	$ (498,074)	$ (516,992)	$ (498,074)
Common stock repurchases (in shares)		100				396
Common stock repurchases		$ (5,229)				$ (15,550)
Employee stock plans (in shares)	23	3	1	76	1	2
Employee stock plans	$ (1,165)	$ (123)	$ (68)	$ (3,039)	$ (53)	$ (84)
Balance at end of period (in shares)	13,657	13,634	13,531	13,526	13,450	13,449	13,657	13,526
Balance at end of period	$ (523,577)	$ (522,412)	$ (517,060)	$ (516,800)	$ (513,761)	$ (513,708)	$ (523,577)	$ (516,800)
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	1,547,435	1,531,065	1,519,811	1,503,049	1,510,688	1,489,176	1,519,811	1,489,176
Comprehensive income	27,863	24,491	19,382	15,358	567	29,733
Dividends declared	(8,099)	(8,090)	(8,104)	(8,097)	(8,072)	(8,133)
Employee stock plans	(86)	(31)	(24)	(14)	(134)	(88)
Balance at end of period	1,567,113	1,547,435	1,531,065	1,510,296	1,503,049	1,510,688	1,567,113	1,510,296
Accumulated Other Non-Owner Changes to Equity
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	(142,626)	(167,217)	(122,315)	(227,640)	(244,684)	(210,495)	(122,315)	(210,495)
Comprehensive income	(21,681)	24,591	(44,902)	42,139	17,044	(34,189)
Balance at end of period	$ (164,307)	$ (142,626)	$ (167,217)	$ (185,501)	$ (227,640)	$ (244,684)	$ (164,307)	$ (185,501)