Consolidated Statements of Changes In Shareholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Class A Common Stock	Class B Common Stock	Common Stock	Common Stock Class A Common Stock	Common Stock Class B Common Stock	Surplus	Surplus Class A Common Stock	Surplus Class B Common Stock	Retained Earnings [Member]	Retained Earnings [Member] Class A Common Stock	Retained Earnings [Member] Class B Common Stock	Accumulated Other Comprehensive Loss	Accumulated Other Comprehensive Loss Class A Common Stock	Accumulated Other Comprehensive Loss Class B Common Stock
Beginning balance at Dec. 31, 2011	$ 1,861,128				$ 8,644	$ 1,640	$ 143,766			$ 1,773,652			$ (66,574)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of accounting change	(2,430)									(2,430)
Net income	132,395				0	0	0			132,395			0
Net current period other comprehensive income	(15,532)				0	0	0			0			(15,532)
Repurchase of common stock shares		(9,131)	(94,493)		(56)	(607)		0	0		(9,075)	(93,886)		0	0
Repurchase and retirement of common stock	0
Cash dividends	(12,313)				0	0	0			(12,313)			0
Ending balance at Dec. 31, 2012	1,859,624				8,588	1,033	143,766			1,788,343			(82,106)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	166,869				0	0	0			166,869			0
Net current period other comprehensive income	56,838				0	0	0			0			56,838
Repurchase of common stock shares		(321)			(2)			0			(319)			0
Repurchase and retirement of common stock	0
Cash dividends	(11,548)				0	0	0			(11,548)			0
Ending balance at Dec. 31, 2013	2,071,462				8,586	1,033	143,766			1,943,345			(25,268)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	138,562				0	0	0			138,562			0
Net current period other comprehensive income	(27,713)				0	0	0			0			(27,713)
Stock Issued During Period, Value, New Issues	563,628				2,587	18	561,023			0			0
Repurchase and retirement of common stock	46,085	36,308	9,777	0	168	46		36,140	9,731		0	0		0	0
Cash dividends	(12,260)				0	0	0			(12,260)			0
Ending balance at Dec. 31, 2014	$ 2,687,594				$ 11,005	$ 1,005	$ 658,918			$ 2,069,647			$ (52,981)