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 (As Originally Reported) at Dec. 31, 2016		$ 3,916,795		$ 422,839
Balance, value at Dec. 31, 2016		3,875,082	$ 3,515,299	381,126	$ (21,343)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income, Note 1 | As Originally Reported		246,019
Net income, Note 1		242,313		242,313
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		$ 3,969,367	$ 3,517,258	477,101	(24,992)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income, Note 1		144,971		144,971
Other comprehensive income, net of tax		(36,808)			(36,808)
Stock-based compensation		3,379	$ 3,379
Stock repurchased and retired, shares			(536,327)
Stock repurchased and retired, value		(12,507)	$ (12,507)
Issuances of common stock under stock plans, shares			592,194
Issuances of common stock under stock plans, value		1,016	$ 1,016
Cash dividends on common stock		$ (88,331)		(88,331)
Balance, shares at Jun. 30, 2018		220,204,691	220,204,691
Balance, value at Jun. 30, 2018		$ 3,981,087	$ 3,509,146	$ 524,031	$ (52,090)

[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.