Consolidated Statements of Changes In Shareholders' Equity (USD $) In Thousands, unless otherwise specified	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	Surplus Class B Common Stock	Retained Earnings	Retained Earnings Class A Common Stock	Retained Earnings 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]
Net income	112,602				0	0	0			112,602			0
Net current period other comprehensive income	14,588				0	0	0			0			14,588
Repurchase of common stock shares			(2,535)	(2,414)	(15)	(13)		0	0		(2,520)	(2,401)		0	0
Cash dividends	(9,245)				0	0	0			(9,245)			0
Ending balance at Sep. 30, 2012	1,974,124				8,629	1,627	143,766			1,872,088			(51,986)
Beginning balance at Dec. 31, 2012	1,864,007	[1]			8,588	1,033	143,766			1,792,726			(82,106)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	140,473				0	0	0			140,473			0
Net current period other comprehensive income	(13,439)				0	0	0			0			(13,439)
Repurchase of common stock shares			(321)		(2)			0			(319)			0
Cash dividends	(8,663)				0	0	0			(8,663)			0
Ending balance at Sep. 30, 2013	$ 1,982,057	[2]			$ 8,586	$ 1,033	$ 143,766			$ 1,924,217			$ (95,545)

[1] Derived from 2012 Annual Report on Form 10-K.

[2] Unaudited