Consolidated Statements of Stockholders' Equity - USD ($)	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated other comprehensive Income (loss)	Treasury Stock	Total
Increase (Decrease) in Stockholders' Equity
Adoption of Accounting Standards Update No. 2018-02			$ 20,068,000	$ (20,068,000)
Balance, beginning at Dec. 31, 2017	$ 1,396,000	$ 2,488,643,000	139,177,000	(96,383,000)	$ (282,000)	$ 2,532,551,000
Balance (in shares) at Dec. 31, 2017	139,588,782
Increase (Decrease) in Stockholders' Equity
Net income			137,011,000			137,011,000
Cash dividends declared			(66,296,000)			(66,296,000)
Equity-based awards		3,671,000	(345,000)			3,326,000
Equity-based awards (in shares)	9,006
Other comprehensive income (loss), net of tax				(65,959,000)		(65,959,000)
Common stock issued under Employee Stock Purchase Plan		342,000				342,000
Common stock issued under Employee Stock Purchase Plan (in shares)	12,341
Common stock repurchased					(81,800,000)	(81,800,000)
Common stock repurchased (in shares)	(2,968,069)
Balance, ending at Jun. 30, 2018	$ 1,396,000	2,492,656,000	229,615,000	(182,410,000)	(82,082,000)	2,459,175,000
Balance (in shares) at Jun. 30, 2018	136,642,060
Balance, beginning at Mar. 31, 2018	$ 1,396,000	2,490,910,000	193,522,000	(164,684,000)	(282,000)	2,520,862,000
Balance (in shares) at Mar. 31, 2018	139,601,123
Increase (Decrease) in Stockholders' Equity
Net income			69,053,000			69,053,000
Cash dividends declared			(32,792,000)			(32,792,000)
Equity-based awards		1,746,000	(168,000)			1,578,000
Equity-based awards (in shares)	9,006
Other comprehensive income (loss), net of tax				(17,726,000)		(17,726,000)
Common stock repurchased					(81,800,000)	(81,800,000)
Common stock repurchased (in shares)	(2,968,069)
Balance, ending at Jun. 30, 2018	$ 1,396,000	2,492,656,000	229,615,000	(182,410,000)	(82,082,000)	2,459,175,000
Balance (in shares) at Jun. 30, 2018	136,642,060
Balance, beginning at Dec. 31, 2018	$ 1,397,000	2,495,853,000	291,919,000	(132,195,000)	(132,135,000)	$ 2,524,839,000
Balance (in shares) at Dec. 31, 2018	134,874,302					134,874,302
Increase (Decrease) in Stockholders' Equity
Net income			142,357,000			$ 142,357,000
Cash dividends declared			(69,984,000)			(69,984,000)
Equity-based awards	$ 2,000	4,093,000	(544,000)		(1,533,000)	2,018,000
Equity-based awards (in shares)	143,756
Other comprehensive income (loss), net of tax				100,211,000		100,211,000
Common stock repurchased					(40,000,000)	(40,000,000)
Common stock repurchased (in shares)	(1,509,846)
Balance, ending at Jun. 30, 2019	$ 1,399,000	2,499,946,000	363,748,000	(31,984,000)	(173,668,000)	$ 2,659,441,000
Balance (in shares) at Jun. 30, 2019	133,508,212					133,508,212
Balance, beginning at Mar. 31, 2019	$ 1,399,000	2,497,770,000	326,451,000	(78,754,000)	(133,664,000)	$ 2,613,202,000
Balance (in shares) at Mar. 31, 2019	135,012,015
Increase (Decrease) in Stockholders' Equity
Net income			72,433,000			72,433,000
Cash dividends declared			(34,916,000)			(34,916,000)
Equity-based awards		2,176,000	(220,000)		(4,000)	1,952,000
Equity-based awards (in shares)	6,043
Other comprehensive income (loss), net of tax				46,770,000		46,770,000
Common stock repurchased					(40,000,000)	(40,000,000)
Common stock repurchased (in shares)	(1,509,846)
Balance, ending at Jun. 30, 2019	$ 1,399,000	$ 2,499,946,000	$ 363,748,000	$ (31,984,000)	$ (173,668,000)	$ 2,659,441,000
Balance (in shares) at Jun. 30, 2019	133,508,212					133,508,212