Condensed Consolidated Statements of Changes In Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Balance, shares at Dec. 31, 2017		220,148,824
Balance, value at Dec. 31, 2017	$ 3,969,367	$ 3,517,258	$ 477,101	$ (24,992)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	78,972		78,972
Other comprehensive income, net of tax	(32,672)			(32,672)
Stock-based compensation	1,829	$ 1,829
Stock repurchased and retired, shares		(201,473)
Stock repurchased and retired	(4,340)	$ (4,340)
Issuances of common stock under stock plans, shares		513,485
Issuances of common stock under stock plans	759	$ 759
Cash dividends on common stock	(44,149)		44,149
Balance, shares at Mar. 31, 2018		220,460,836
Balance, value at Mar. 31, 2018	3,969,766	$ 3,515,506	502,214	(47,954)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	65,999		65,999
Other comprehensive income, net of tax	(4,136)			(4,136)
Stock-based compensation	1,550	$ 1,550
Stock repurchased and retired, shares		(334,854)
Stock repurchased and retired	(8,167)	$ (8,167)
Issuances of common stock under stock plans, shares		78,709
Issuances of common stock under stock plans	257	$ 257
Cash dividends on common stock	(44,182)		(44,182)
Balance, shares at Jun. 30, 2018		220,204,691
Balance, value at Jun. 30, 2018	3,981,087	$ 3,509,146	524,031	(52,090)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	90,981		90,981
Other comprehensive income, net of tax	(23,585)			(23,585)
Stock-based compensation	2,140	$ 2,140
Stock repurchased and retired, shares		(17,784)
Stock repurchased and retired	(386)	$ (386)
Issuances of common stock under stock plans, shares		51,324
Issuances of common stock under stock plans	49	$ 49
Cash dividends on common stock	(46,393)		(46,393)
Balance, shares at Sep. 30, 2018		220,238,231
Balance, value at Sep. 30, 2018	4,003,893	$ 3,510,949	568,619	(75,675)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	80,311		80,311
Other comprehensive income, net of tax	16,761			16,761
Stock-based compensation	1,994	$ 1,994
Stock repurchased and retired, shares		(3,537)
Stock repurchased and retired	(69)	$ (69)
Issuances of common stock under stock plans, shares		20,345
Issuances of common stock under stock plans	0	$ 0
Cash dividends on common stock	$ (46,448)		(46,448)
Balance, shares at Dec. 31, 2018	220,255,039	220,255,039
Balance, value at Dec. 31, 2018	$ 4,056,442	$ 3,512,874	602,482	(58,914)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	74,033		74,033
Other comprehensive income, net of tax	29,632			29,632
Stock-based compensation	754	$ 754
Stock repurchased and retired, shares		(108,088)
Stock repurchased and retired	(1,918)	$ (1,918)
Issuances of common stock under stock plans, shares		310,257
Issuances of common stock under stock plans	21	$ 21
Cash dividends on common stock	$ (46,394)		(46,394)
Balance, shares at Mar. 31, 2019	220,457,208	220,457,208.000
Balance, value at Mar. 31, 2019	$ 4,112,326	$ 3,511,731	$ 629,877	$ (29,282)