Condensed Consolidated Statements of Changes In Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2017		220,148,824
Beginning balance 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 loss, net of tax	(32,672)			(32,672)
Stock-based compensation	1,829	$ 1,829
Stock repurchased and retired (in shares)		(201,473)
Stock repurchased and retired	(4,340)	$ (4,340)
Issuances of common stock under stock plans (in shares)		513,485
Issuances of common stock under stock plans	759	$ 759
Cash dividends on common stock	$ (44,149)		(44,149)
Cash dividends on common stock (in dollars per share)	$ 0.20
Ending balance (in shares) at Mar. 31, 2018		220,460,836
Ending balance at Mar. 31, 2018	$ 3,969,766	$ 3,515,506	502,214	(47,954)
Beginning balance (in shares) at Dec. 31, 2017		220,148,824
Beginning balance at Dec. 31, 2017	3,969,367	$ 3,517,258	477,101	(24,992)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	235,952
Other comprehensive loss, net of tax	(60,393)
Ending balance (in shares) at Sep. 30, 2018		220,238,231
Ending balance at Sep. 30, 2018	4,003,893	$ 3,510,949	568,619	(75,675)
Beginning balance (in shares) at Mar. 31, 2018		220,460,836
Beginning balance 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 loss, net of tax	(4,136)			(4,136)
Stock-based compensation	1,550	$ 1,550
Stock repurchased and retired (in shares)		(334,854)
Stock repurchased and retired	(8,167)	$ (8,167)
Issuances of common stock under stock plans (in shares)		78,709
Issuances of common stock under stock plans	257	$ 257
Cash dividends on common stock	$ (44,182)		(44,182)
Cash dividends on common stock (in dollars per share)	$ 0.20
Ending balance (in shares) at Jun. 30, 2018		220,204,691
Ending balance 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 loss, net of tax	(23,585)			(23,585)
Stock-based compensation	2,140	$ 2,140
Stock repurchased and retired (in shares)		(17,784)
Stock repurchased and retired	(386)	$ (386)
Issuances of common stock under stock plans (in shares)		51,324
Issuances of common stock under stock plans	49	$ 49
Cash dividends on common stock	$ (46,393)		(46,393)
Cash dividends on common stock (in dollars per share)	$ 0.21
Ending balance (in shares) at Sep. 30, 2018		220,238,231
Ending balance 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 loss, net of tax	16,761			16,761
Stock-based compensation	1,994	$ 1,994
Stock repurchased and retired (in shares)		(3,537)
Stock repurchased and retired	(69)	$ (69)
Issuances of common stock under stock plans (in shares)		20,345
Issuances of common stock under stock plans	0	$ 0
Cash dividends on common stock	$ (46,448)		(46,448)
Cash dividends on common stock (in dollars per share)	$ 0.21
Ending balance (in shares) at Dec. 31, 2018	220,255,039	220,255,039
Ending balance 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 loss, net of tax	29,632			29,632
Stock-based compensation	754	$ 754
Stock repurchased and retired (in shares)		(108,088)
Stock repurchased and retired	(1,918)	$ (1,918)
Issuances of common stock under stock plans (in shares)		310,257
Issuances of common stock under stock plans	21	$ 21
Cash dividends on common stock	$ (46,394)		(46,394)
Cash dividends on common stock (in dollars per share)	$ 0.21
Ending balance (in shares) at Mar. 31, 2019		220,457,208
Ending balance at Mar. 31, 2019	$ 4,112,326	$ 3,511,731	629,877	(29,282)
Beginning balance (in shares) at Dec. 31, 2018	220,255,039	220,255,039
Beginning balance at Dec. 31, 2018	$ 4,056,442	$ 3,512,874	602,482	(58,914)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	270,345
Other comprehensive loss, net of tax	$ 103,878
Ending balance (in shares) at Sep. 30, 2019	220,212,134	220,212,134
Ending balance at Sep. 30, 2019	$ 4,289,516	$ 3,511,493	733,059	44,964
Beginning balance (in shares) at Mar. 31, 2019		220,457,208
Beginning balance at Mar. 31, 2019	4,112,326	$ 3,511,731	629,877	(29,282)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	111,810		111,810
Other comprehensive loss, net of tax	48,395			48,395
Stock-based compensation	2,722	$ 2,722
Stock repurchased and retired (in shares)		(4,113)
Stock repurchased and retired	(62)	$ (62)
Issuances of common stock under stock plans (in shares)		45,589
Issuances of common stock under stock plans	0	$ 0
Cash dividends on common stock	$ (46,684)		(46,684)
Cash dividends on common stock (in dollars per share)	$ 0.21
Ending balance (in shares) at Jun. 30, 2019		220,498,684
Ending balance at Jun. 30, 2019	$ 4,228,507	$ 3,514,391	695,003	19,113
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	84,502		84,502
Other comprehensive loss, net of tax	25,851			25,851
Stock-based compensation	2,350	$ 2,350
Stock repurchased and retired (in shares)		(300,719)
Stock repurchased and retired	(5,248)	$ (5,248)
Issuances of common stock under stock plans (in shares)		14,169
Issuances of common stock under stock plans	0	$ 0
Cash dividends on common stock	$ (46,446)		(46,446)
Cash dividends on common stock (in dollars per share)	$ 0.21
Ending balance (in shares) at Sep. 30, 2019	220,212,134	220,212,134
Ending balance at Sep. 30, 2019	$ 4,289,516	$ 3,511,493	$ 733,059	$ 44,964