Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]
Beginning Balance at Dec. 31, 2018	$ 2,247,573	$ 554,377	$ 1,489,703	$ 946,032	$ (59,063)	$ (683,476)
Beginning Balance (in shares) at Dec. 31, 2018		170,184
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	116,442			116,442
Other comprehensive income	46,906				46,906
Stock issued (in shares)		544
Stock issued	1,653	$ 1,313	577			(237)
Stock-based compensation awards (in shares)
Stock-based compensation awards	3,348		3,348
Acquisition of treasury stock (in shares)		(3,825)
Acquisition of treasury stock (in shares)	(63,386)					(63,386)
Common stock cash dividends	(43,738)			(43,738)
Ending Balance at Jun. 30, 2019	2,308,798	$ 555,690	1,493,628	1,018,736	(12,157)	(747,099)
Ending Balance (in shares) at Jun. 30, 2019		166,903
Beginning Balance at Mar. 31, 2019	2,301,019	$ 554,485	1,491,870	980,708	(37,633)	(688,411)
Beginning Balance (in shares) at Mar. 31, 2019		169,923
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	59,779			59,779
Other comprehensive income	25,476				25,476
Stock issued (in shares)		429
Stock issued	(4)	$ 1,205	(30)			(1,179)
Stock-based compensation awards (in shares)
Stock-based compensation awards	1,788		1,788
Acquisition of treasury stock (in shares)		(3,449)
Acquisition of treasury stock (in shares)	(57,509)					(57,509)
Common stock cash dividends	(21,751)			(21,751)
Ending Balance at Jun. 30, 2019	2,308,798	$ 555,690	1,493,628	1,018,736	(12,157)	(747,099)
Ending Balance (in shares) at Jun. 30, 2019		166,903
Beginning Balance at Dec. 31, 2019	2,342,176	$ 556,110	1,499,681	1,079,391	(137)	(792,869)
Beginning Balance (in shares) at Dec. 31, 2019		164,218
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	65,606			65,606
Other comprehensive income	51,576				51,576
Stock issued (in shares)		648
Stock issued	3,198	$ 1,459	540			1,200
Stock-based compensation awards (in shares)
Stock-based compensation awards	3,530		3,530
Acquisition of treasury stock (in shares)		(2,908)
Acquisition of treasury stock (in shares)	(39,748)					(39,748)
Common stock cash dividends	(42,030)			(42,030)
Ending Balance at Jun. 30, 2020	2,340,501	$ 557,569	1,503,750	1,059,160	51,439	(831,417)
Ending Balance (in shares) at Jun. 30, 2020		161,958
Beginning Balance at Mar. 31, 2020	2,285,748	$ 556,243	1,502,189	1,040,646	18,308	(831,638)
Beginning Balance (in shares) at Mar. 31, 2020		161,435
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	39,559
Other comprehensive income	33,131				33,131
Stock issued (in shares)		523
Stock issued	1,197	$ 1,326	(350)			221
Stock-based compensation awards (in shares)
Stock-based compensation awards	1,911		1,911
Common stock cash dividends	(21,045)			(21,045)
Ending Balance at Jun. 30, 2020	$ 2,340,501	$ 557,569	$ 1,503,750	$ 1,059,160	$ 51,439	$ (831,417)
Ending Balance (in shares) at Jun. 30, 2020		161,958