Consolidated Statements of Changes In Shareholders' Equity - USD ($) $ in Thousands	Total	Class A Common Stock	Class B Common Stock	Common Stock Class A Common Stock	Common Stock Class B Common Stock	Surplus	Surplus Class A Common Stock	Retained Earnings	Retained Earnings Class A Common Stock	Retained Earnings Class B Common Stock	Accumulated Other Comprehensive (Loss) Income	Financial Instruments ASU cumulative effect adjustment Retained Earnings	Financial Instruments ASU cumulative effect adjustment Accumulated Other Comprehensive (Loss) Income	Income tax ASU cumulative effect adjustment Retained Earnings	Income tax ASU cumulative effect adjustment Accumulated Other Comprehensive (Loss) Income
Shareholders' equity	$ 3,334,064			$ 11,005	$ 1,005	$ 658,918		$ 2,785,430			$ (122,294)
Net income	193,522							193,522
Other comprehensive income (loss), net of tax	(72,293)										(72,293)
Cash dividends		$ (7,703)	$ (704)						$ (7,703)	$ (704)
Shareholders' equity	3,372,114			11,005	1,005	658,918		2,931,509			(230,323)
Net income	93,291							93,291
Other comprehensive income (loss), net of tax	(14,315)										(14,315)
Cash dividends		(3,852)	(352)						(3,852)	(352)
Cumulative effect of new accounting principle in period of adoption												$ 18,715	$ (18,715)	$ 31,336	$ (31,336)
Shareholders' equity	3,446,886			11,005	1,005	658,918		3,020,596			(244,638)
Shareholders' equity	3,488,954			10,623	1,005	493,962		3,218,551			(235,187)
Net income	230,718
Other comprehensive income (loss), net of tax	54,456										54,456
Stock repurchased during period	(190,500)	(190,530)		(448)			$ (190,082)
Cash dividends		(8,181)	(804)						(8,181)	(804)
Shareholders' equity	3,523,309			10,380	1,005	393,449		3,325,335			(206,860)
Net income	119,359							119,359
Other comprehensive income (loss), net of tax	26,129										26,129
Stock repurchased during period	(89,800)	(89,774)		(205)			$ (89,569)
Cash dividends		$ (4,008)	$ (402)						$ (4,008)	$ (402)
Shareholders' equity	$ 3,574,613			$ 10,175	$ 1,005	$ 303,880		$ 3,440,284			$ (180,731)