CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands		Total	Common Stock	Preferred Stock	Surplus		Retained earnings	Treasury Stock	Accumulated other comprehensive income (loss)
Beginning Balance at Dec. 31, 2017		$ 5,103,905	$ 1,042	$ 50,160	$ 4,298,503		$ 1,194,994	$ (90,142)	$ (350,652)
Increase Decrease In Stockholders Equity [Roll Forward]
Net income		511,755					511,755
Issuance of stock		2,565	1		2,564
Dividends declared:
Common stock	[1]	(76,200)					(76,200)
Preferred stock		(2,792)					(2,792)
Common stock purchases		(127,443)			(23,020)	[2]		(104,423)
Common stock reissuance		2,151			143			2,008
Stock based compensation		12,010			3,325			8,685
Other comprehensive loss, net of tax		(183,537)							(183,537)
Ending Balance at Sep. 30, 2018		5,244,349	1,043	50,160	4,281,515		1,629,692	(183,872)	(534,189)
Beginning Balance at Jun. 30, 2018		5,289,661	1,043	50,160	4,302,946		1,515,058	(82,754)	(496,792)
Increase Decrease In Stockholders Equity [Roll Forward]
Net income		140,648					140,648
Issuance of stock		822			822
Dividends declared:
Common stock	[3]	(25,084)					(25,084)
Preferred stock		(930)					(930)
Common stock purchases		(125,099)			(23,020)			(102,079)
Common stock reissuance		814			103			711
Stock based compensation		914			664			250
Other comprehensive loss, net of tax		(37,397)							(37,397)
Ending Balance at Sep. 30, 2018		5,244,349	1,043	50,160	4,281,515		1,629,692	(183,872)	(534,189)
Increase Decrease In Stockholders Equity [Roll Forward]
Cumulative effect of accounting change		1,935					1,935
Beginning Balance at Dec. 31, 2018		5,435,057	1,043	50,160	4,365,606		1,651,731	(205,509)	(427,974)
Increase Decrease In Stockholders Equity [Roll Forward]
Net income		504,350					504,350
Issuance of stock		2,633	1		2,632
Dividends declared:
Common stock	[1]	(86,996)					(86,996)
Preferred stock		(2,792)					(2,792)
Common stock purchases	[2]	(256,006)			(52,670)			(203,336)
Common stock reissuance		3,890			274			3,616
Stock based compensation		14,313			1,714			12,599
Other comprehensive loss, net of tax		289,094							289,094
Ending Balance at Sep. 30, 2019		5,908,448	1,044	50,160	4,317,556		2,071,198	(392,630)	(138,880)
Beginning Balance at Jun. 30, 2019		5,719,834	1,044	50,160	4,316,225		1,935,826	(392,208)	(191,213)
Increase Decrease In Stockholders Equity [Roll Forward]
Net income		165,319					165,319
Issuance of stock		909	0		909
Dividends declared:
Common stock	[3]	(29,017)					(29,017)
Preferred stock		(930)					(930)
Common stock purchases		(1,367)						(1,367)
Common stock reissuance		964			50			914
Stock based compensation		403			372			31
Other comprehensive loss, net of tax		52,333							52,333
Ending Balance at Sep. 30, 2019		5,908,448	$ 1,044	$ 50,160	$ 4,317,556		2,071,198	$ (392,630)	$ (138,880)
Increase Decrease In Stockholders Equity [Roll Forward]
Cumulative effect of accounting change		$ 4,905					$ 4,905

[1] Dividends declared per common share during the nine months ended September 30, 2019 - $0.90 (2018 - $0.75).

[2] On February 28, 2019, the Corporation entered into a $250 million accelerated share repurchase transaction with respect to its common stock, which was accounted for as a treasury stock transaction. Refer to Note 19 for additional information.

[3] Dividends declared per common share during the quarter ended September 30, 2019 - $0.30 (2018 - $0.25).