Condensed Consolidated Statements of Changes In Shareholders' Equity (Unaudited) - USD ($) $ in Thousands		Total	Common stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Previously Reported [Member]	Previously Reported [Member] Retained Earnings	Adjustment
Balance, shares at Dec. 31, 2016			220,177,030
Balance, value at Dec. 31, 2016		$ 3,875,082	$ 3,515,299	$ 381,126	$ (21,343)	$ 3,916,795	$ 422,839
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		46,036		46,036		46,003		$ 33
Other comprehensive income, net of tax		2,539			2,539
Stock-based compensation		2,804	$ 2,804
Stock repurchased and retired, shares			(99,033)
Stock repurchased and retired, value		(1,796)	$ (1,796)
Issuances of common stock under stock plans, shares			271,114
Issuances of common stock under stock plans, value		230	$ 230
Cash dividends on common stock		(35,425)		(35,425)
Balance, shares at Mar. 31, 2017			220,349,111
Balance, value at Mar. 31, 2017		3,889,470	$ 3,516,537	391,737	(18,804)
Balance, shares at Dec. 31, 2016			220,177,030
Balance, value at Dec. 31, 2016		3,875,082	$ 3,515,299	381,126	(21,343)	3,916,795	$ 422,839
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		167,062				164,148		2,914
Other comprehensive income, net of tax		13,819
Balance, shares at Sep. 30, 2017			220,225,406
Balance, value at Sep. 30, 2017		3,946,461	$ 3,516,558	437,427	(7,524)
Balance, shares at Mar. 31, 2017			220,349,111
Balance, value at Mar. 31, 2017		3,889,470	$ 3,516,537	391,737	(18,804)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		57,219		57,219		56,812		407
Other comprehensive income, net of tax		8,753			8,753
Stock-based compensation		1,471	$ 1,471
Stock repurchased and retired, shares			(239,979)
Stock repurchased and retired, value		(4,147)	$ (4,147)
Issuances of common stock under stock plans, shares			95,383
Issuances of common stock under stock plans, value		233	$ 233
Cash dividends on common stock		(35,427)		(35,427)
Balance, shares at Jun. 30, 2017			220,204,515
Balance, value at Jun. 30, 2017		3,917,572	$ 3,514,094	413,529	(10,051)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		63,807		63,807		61,333		2,474
Other comprehensive income, net of tax		2,527			2,527
Stock-based compensation		2,413	$ 2,413
Stock repurchased and retired, shares			(1,837)
Stock repurchased and retired, value		(34)	$ (34)
Issuances of common stock under stock plans, shares			22,728
Issuances of common stock under stock plans, value		85	$ 85
Cash dividends on common stock		(39,909)		(39,909)
Balance, shares at Sep. 30, 2017			220,225,406
Balance, value at Sep. 30, 2017		3,946,461	$ 3,516,558	437,427	(7,524)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		75,251		75,251		$ 81,871		$ (6,620)
Other comprehensive income, net of tax		(13,038)			(13,038)
Stock-based compensation		2,924	$ 2,924
Stock repurchased and retired, shares			(127,706)
Stock repurchased and retired, value		(2,637)	$ (2,637)
Issuances of common stock under stock plans, shares			51,124
Issuances of common stock under stock plans, value		413	$ 413
Cash dividends on common stock		(40,007)		(40,007)
Tax rate effect reclassification	[1]	$ 0		4,430	(4,430)
Balance, shares at Dec. 31, 2017		220,148,824	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, value		(4,340)	$ (4,340)
Issuances of common stock under stock plans, shares			513,485
Issuances of common stock under stock plans, value		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)
Balance, shares at Dec. 31, 2017		220,148,824	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		235,952
Other comprehensive income, net of tax		$ (60,393)
Balance, shares at Sep. 30, 2018		220,238,231	220,238,231
Balance, value at Sep. 30, 2018		$ 4,003,893	$ 3,510,949	568,619	(75,675)
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, value		(8,167)	$ (8,167)
Issuances of common stock under stock plans, shares			78,709
Issuances of common stock under stock plans, value		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, value		(386)	$ (386)
Issuances of common stock under stock plans, shares			51,324
Issuances of common stock under stock plans, value		49	$ 49
Cash dividends on common stock		$ (46,393)		(46,393)
Balance, shares at Sep. 30, 2018		220,238,231	220,238,231
Balance, value at Sep. 30, 2018		$ 4,003,893	$ 3,510,949	$ 568,619	$ (75,675)

[1] The reclassification adjustment from accumulated other comprehensive income (loss) to retained earnings relating to the effects from the application of the Tax Cuts and Jobs Act of 2017.