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
Beginning 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		169,736			169,736
Other comprehensive income (loss)		4,628					4,628
Stock compensation costs		5,151		5,151
Net activity of common stock pursuant to various stock compensation plans and agreements (in shares)			294,115
Net activity of common stock pursuant to various stock compensation plans and agreements		(12,154)		0
Net activity of common stock pursuant to various stock compensation plans and agreements						(12,154)
Cash dividends on common stock		(29,148)			(29,148)
Ending balance (in shares) at Mar. 31, 2017			144,461,566
Ending balance at Mar. 31, 2017		3,565,954		1,732,749	2,328,264	(451,541)	(43,518)
Increase (Decrease) in Stockholders' Equity
Cumulative effect of change in accounting principle related to marketable equity securities	[1]	(160)			(545)		385
Beginning 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
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate	[2]				6,656		(6,656)
Net income		187,032			187,032
Other comprehensive income (loss)		(12,014)					(12,014)
Stock compensation costs		6,158		6,158
Net activity of common stock pursuant to various stock compensation plans and agreements (in shares)			329,465
Net activity of common stock pursuant to various stock compensation plans and agreements		(14,946)		(14,946)
Net activity of common stock pursuant to various stock compensation plans and agreements						0
Cash dividends on common stock		(29,266)			(29,266)
Ending balance (in shares) at Mar. 31, 2018			144,872,525
Ending balance at Mar. 31, 2018		$ 3,978,755		$ 1,746,707	$ 2,740,179	$ (452,327)	$ (55,804)

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

[2] 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 during the first quarter of 2018. Refer to Note 2 — Current Accounting Developments to the Consolidated Financial Statements for additional information.