Consolidated Statements of Changes In Shareholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Class A 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	Accumulated Other Comprehensive Loss	Accumulated Other Comprehensive Loss Class A Common Stock
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	55,585		0	0	0		55,585		0
Net current period other comprehensive income	2,201		0	0	0		0		2,201
Repurchase of common stock shares		(321)	(2)			0		(319)		0
Cash dividends	(2,891)		0	0	0		(2,891)		0
Ending balance at Mar. 31, 2013	1,918,581		8,586	1,033	143,766		1,845,101		(79,905)
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	22,366		0	0	0		22,366		0
Net current period other comprehensive income	8,674		0	0	0		0		8,674
Cash dividends	(2,885)		0	0	0		(2,885)		0
Ending balance at Mar. 31, 2014	$ 2,104,830		$ 8,586	$ 1,033	$ 143,766		$ 1,968,039		$ (16,594)