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		371,107				371,107
Issuance of stock		1,743	1		1,742
Dividends declared:
Common stock	[1]	(51,116)				(51,116)
Preferred stock		(1,862)				(1,862)
Common stock purchases		(2,344)					(2,344)
Common stock reissuance		1,337			40		1,297
Stock based compensation		11,096			2,661		8,435
Other comprehensive loss, net of tax		(146,140)						(146,140)
Ending Balance at Jun. 30, 2018		5,289,661	1,043	50,160	4,302,946	1,515,058	(82,754)	(496,792)
Beginning Balance at Mar. 31, 2018		5,064,909	1,043	50,160	4,300,936	1,261,775	(86,167)	(462,838)
Increase Decrease In Stockholders Equity [Roll Forward]
Net Income		279,783				279,783
Issuance of stock		862			862
Dividends declared:
Common stock	[2]	(25,569)				(25,569)
Preferred stock		(931)				(931)
Common stock purchases		(1,016)					(1,016)
Common stock reissuance		615			56		559
Stock based compensation		4,962			1,092		3,870
Other comprehensive loss, net of tax		(33,954)						(33,954)
Ending 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]
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		339,031				339,031
Issuance of stock		1,724	1		1,723
Dividends declared:
Common stock	[1]	(57,979)				(57,979)
Preferred stock		(1,862)				(1,862)
Common stock purchases	[3]	(254,639)			(52,670)		(201,969)
Common stock reissuance		2,926			224		2,702
Stock based compensation		13,910			1,342		12,568
Other comprehensive loss, net of tax		236,761						236,761
Ending Balance at Jun. 30, 2019		5,719,834	1,044	50,160	4,316,225	1,935,826	(392,208)	(191,213)
Beginning Balance at Mar. 31, 2019		5,440,060	1,043	50,160	4,313,040	1,794,644	(394,848)	(323,979)
Increase Decrease In Stockholders Equity [Roll Forward]
Net Income		171,106				171,106
Issuance of stock		931	1		930
Dividends declared:
Common stock	[2]	(28,993)				(28,993)
Preferred stock		(931)				(931)
Common stock purchases		(1,520)					(1,520)
Common stock reissuance		743			46		697
Stock based compensation		5,672			2,209		3,463
Other comprehensive loss, net of tax		132,766						132,766
Ending 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]
Cumulative effect of accounting change		$ 4,905				$ 4,905

[1] Dividends declared per common share during the six months ended June 30, 2019 - $0.60 (2018 - $0.50).

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

[3] 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 18 for additional information.