Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Common Stock and Additional Paid-in Capital	Retained Earnings	Treasury Stock	AOCI, net of tax
BALANCE (in shares) at Dec. 31, 2015		143,909,233
Beginning balance at Dec. 31, 2015	$ 3,122,950		$ 1,701,459	$ 1,872,594	$ (436,162)	$ (14,941)
Increase (Decrease) in Stockholders' Equity
Net income	210,800			210,800
Other comprehensive income	13,229					13,229
Stock compensation costs	9,210		9,210
Net activity of common stock pursuant to various stock compensation plans and agreements (in shares)		192,912
Net activity of common stock pursuant to various stock compensation plans and agreements	(1,027)		2,067
Net activity of common stock pursuant to various stock compensation plans and agreements					(3,094)
Common stock dividends	(58,252)			(58,252)
BALANCE (in shares) at Jun. 30, 2016		144,102,145
Ending balance at Jun. 30, 2016	3,296,910		1,712,736	2,025,142	(439,256)	(1,712)
Beginning balance at Mar. 31, 2016						(2,058)
Increase (Decrease) in Stockholders' Equity
Net income	103,284
Other comprehensive income	346
BALANCE (in shares) at Jun. 30, 2016		144,102,145
Ending balance at Jun. 30, 2016	3,296,910		1,712,736	2,025,142	(439,256)	(1,712)
BALANCE (in shares) at Dec. 31, 2016		144,167,451
Beginning balance at Dec. 31, 2016	3,427,741		1,727,598	2,187,676	(439,387)	(48,146)
Increase (Decrease) in Stockholders' Equity
Net income	288,066			288,066
Other comprehensive income	13,965					13,965
Stock compensation costs	10,115		10,115
Net activity of common stock pursuant to various stock compensation plans and agreements (in shares)		318,875
Net activity of common stock pursuant to various stock compensation plans and agreements	(11,251)		1,008
Net activity of common stock pursuant to various stock compensation plans and agreements					(12,259)
Common stock dividends	(58,375)			(58,375)
BALANCE (in shares) at Jun. 30, 2017		144,486,326
Ending balance at Jun. 30, 2017	3,670,261		1,738,721	2,417,367	(451,646)	(34,181)
Beginning balance at Mar. 31, 2017						(43,518)
Increase (Decrease) in Stockholders' Equity
Net income	118,330
Other comprehensive income	9,337
BALANCE (in shares) at Jun. 30, 2017		144,486,326
Ending balance at Jun. 30, 2017	$ 3,670,261		$ 1,738,721	$ 2,417,367	$ (451,646)	$ (34,181)