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, 2016			220,177,030
Balance, value at Dec. 31, 2016		$ 3,916,795	$ 3,515,299	$ 422,839	$ (21,343)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		246,019		246,019
Other comprehensive income, net of tax		781			781
Stock-based compensation		9,612	$ 9,612
Stock repurchased and retired, shares			(468,555)
Stock repurchased and retired, value		(8,614)	$ (8,614)
Issuances of common stock under stock plans, shares			440,349
Issuances of common stock under stock plans, value		961	$ 961
Cash dividends on common stock		(150,768)		(150,768)
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		$ 4,014,786	$ 3,517,258	522,520	(24,992)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		77,669		77,669
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	220,460,836
Balance, value at Mar. 31, 2018		$ 4,013,882	$ 3,515,506	546,330	(47,954)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect of New Accounting Principle in Period of Adoption	[2]	$ 0		$ (9,710)	$ 9,710

[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.

[2] The cumulative effect adjustment from retained earnings to accumulated other comprehensive income (loss) relating to the implementation of new accounting guidance for the junior subordinated debentures that the Company previously elected to fair value on a recurring basis. Refer to Note 1 for discussion of the new accounting guidance.