Consolidated Statement 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, 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	384,677			384,677
Other comprehensive income (loss)	(19,178)					(19,178)
Stock compensation costs	16,502		16,502
Net activity of common stock pursuant to various stock compensation plans and agreements (in shares)		327,004
Net activity of common stock pursuant to various stock compensation plans and agreements	1,062		7,026		(5,964)
Cash dividends on common stock	(116,224)			(116,224)
BALANCE (in shares) at Dec. 31, 2015		143,909,233
Ending 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	431,677			431,677
Other comprehensive income (loss)	(33,205)					(33,205)
Stock compensation costs	22,102		22,102
Net activity of common stock pursuant to various stock compensation plans and agreements (in shares)		258,218
Net activity of common stock pursuant to various stock compensation plans and agreements	812		4,037		(3,225)
Cash dividends on common stock	(116,595)			(116,595)
BALANCE (in shares) at Dec. 31, 2016		144,167,451
Ending 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	505,624			505,624
Other comprehensive income (loss)	10,627					10,627
Stock compensation costs	24,657		24,657
Net activity of common stock pursuant to various stock compensation plans and agreements (in shares)		375,609
Net activity of common stock pursuant to various stock compensation plans and agreements	(9,700)		3,240		(12,940)
Cash dividends on common stock	(116,998)			(116,998)
BALANCE (in shares) at Dec. 31, 2017		144,543,060
Ending balance at Dec. 31, 2017	$ 3,841,951		$ 1,755,495	$ 2,576,302	$ (452,327)	$ (37,519)