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	99,491	0	0	0	99,491	0
Net current period other comprehensive income	(18,070)	0	0	0	0	(18,070)
Repurchase of common stock shares	(321)	(2)			(319)
Cash dividends	(5,777)	0	0	0	(5,777)	0
Ending balance at Jun. 30, 2013	1,939,330	8,586	1,033	143,766	1,886,121	(100,176)
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	48,916	0	0	0	48,916	0
Net current period other comprehensive income	29,325	0	0	0	0	29,325
Cash dividends	(5,771)	0	0	0	(5,771)	0
Ending balance at Jun. 30, 2014	$ 2,149,145	$ 8,586	$ 1,033	$ 143,766	$ 1,991,703	$ 4,057