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
Beginning balance (in shares) at Dec. 31, 2014		143,582,229
Beginning balance at Dec. 31, 2014	$ 2,856,111		$ 1,677,931	$ 1,604,141	$ (430,198)	$ 4,237
Increase (Decrease) in Stockholders' Equity
Net income	198,775			198,775
Other comprehensive income	1,193					1,193
Stock compensation costs	7,652		7,652
Tax benefit from stock compensation plans, net	3,196		3,196
Net activity of common stock pursuant to various stock compensation plans and agreements (in shares)		266,807
Net activity of common stock pursuant to various stock compensation plans and agreements	(4,018)		1,769		(5,787)
Common stock dividends	(57,961)			(57,961)
Ending beginning (in shares) at Jun. 30, 2015		143,849,036
Ending balance at Jun. 30, 2015	3,004,948		1,690,548	1,744,955	(435,985)	5,430
Beginning balance at Mar. 31, 2015						13,555
Increase (Decrease) in Stockholders' Equity
Net income	98,748
Other comprehensive income	(8,125)					(8,125)
Tax benefit from stock compensation plans, net			51
Ending beginning (in shares) at Jun. 30, 2015		143,849,036
Ending balance at Jun. 30, 2015	3,004,948		1,690,548	1,744,955	(435,985)	5,430
Beginning 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
Tax benefit from stock compensation plans, net	1,005		1,005
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	(2,032)		1,062		(3,094)
Common stock dividends	(58,252)			(58,252)
Ending beginning (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					346
Tax benefit from stock compensation plans, net			19
Ending beginning (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)