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, 2014		220,161,120
Balance, value at Dec. 31, 2014	$ 3,777,626	$ 3,519,316	$ 246,242	$ 12,068
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	222,539		222,539
Other comprehensive loss, net of tax	(14,626)			(14,626)
Stock-based compensation	14,383	$ 14,383
Stock repurchased and retired, shares		(844,215)
Stock repurchased and retired, value	(14,589)	$ (14,589)
Issuances of common stock under stock plans and related net tax benefit, shares		854,186
Issuances of common stock under stock plans and related net tax benefit, value	1,481	$ 1,481
Cash dividends on common stock	$ (137,480)		(137,480)
Balance, shares at Dec. 31, 2015	220,171,091	220,171,091
Balance, value at Dec. 31, 2015	$ 3,849,334	$ 3,520,591	331,301	(2,558)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	101,856		101,856
Other comprehensive loss, net of tax	25,218			25,218
Stock-based compensation	5,245	$ 5,245
Stock repurchased and retired, shares		(604,716)
Stock repurchased and retired, value	(9,374)	$ (9,374)
Issuances of common stock under stock plans and related net tax benefit, shares		915,772
Issuances of common stock under stock plans and related net tax benefit, value	778	$ 778
Cash dividends on common stock	$ (70,899)		(70,899)
Balance, shares at Jun. 30, 2016	220,482,147	220,482,147
Balance, value at Jun. 30, 2016	$ 3,902,158	$ 3,517,240	$ 362,258	$ 22,660