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, 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		431,677			431,677
Other comprehensive income (loss)		(33,205)					(33,205)
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		22,914		26,139		(3,225)
Cash dividends on common stock		$ (116,595)			(116,595)
Dividends declared per common share (in dollars per share)		$ 0.80
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
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		14,957		27,897		(12,940)
Cash dividends on common stock		$ (116,998)			(116,998)
Dividends declared per common share (in dollars per share)		$ 0.80
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)
Increase (Decrease) in Stockholders' Equity
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate	[1]	0			6,656		(6,656)
Balance (in shares) at Dec. 31, 2017			144,543,060
Beginning balance at Dec. 31, 2017		3,841,951		1,755,495	2,576,302	(452,327)	(37,519)
Increase (Decrease) in Stockholders' Equity
Net income		703,701			703,701
Other comprehensive income (loss)		(14,384)					(14,384)
Net activity of common stock pursuant to various stock compensation plans and agreements (in shares)			418,303
Net activity of common stock pursuant to various stock compensation plans and agreements		18,848		34,482		(15,634)
Cash dividends on common stock		$ (125,982)			(125,982)
Dividends declared per common share (in dollars per share)		$ 0.86
Balance (in shares) at Dec. 31, 2018			144,961,363
Ending balance at Dec. 31, 2018		$ 4,423,974		$ 1,789,977	3,160,132	$ (467,961)	(58,174)
Increase (Decrease) in Stockholders' Equity
Cumulative effect of change in accounting principle related to marketable equity securities	[2]	$ (160)			$ (545)		$ 385

[1] Represents amounts reclassified from AOCI to retained earnings due to the early adoption of ASU 2018-02, Income Statement — Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income in the first quarter of 2018. Refer to Note 1 — Summary of Significant Accounting Policies to the Consolidated Financial Statements for additional information.

[2] Represents the impact of the adoption of Accounting Standards Update (“ASU”) 2016-01, Financial Instruments — Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities in the first quarter of 2018. Refer to Note 1 — Summary of Significant Accounting Policies to the Consolidated Financial Statements for additional information.