Consolidated Statements of Changes In Shareholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock Class A Common Stock	Common Stock Class B Common Stock	Surplus	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning balance at Dec. 31, 2012	$ 1,864,007	$ 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)			(319)
Cash dividends	(8,663)	0	0	0	(8,663)	0
Ending balance at Sep. 30, 2013	1,982,057	8,586	1,033	143,766	1,924,217	(95,545)
Beginning balance at Dec. 31, 2013	2,076,675	8,586	1,033	143,766	1,948,558	(25,268)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	75,279	0	0	0		0
Net current period other comprehensive income	23,410	0	0	0	0
Cash dividends	(8,657)	0	0	0	(8,657)	0
Ending balance at Sep. 30, 2014	$ 2,166,707	$ 8,586	$ 1,033	$ 143,766	$ 2,015,180	$ (1,858)