Consolidated Statements of Changes In Shareholders' Equity - USD ($) $ in Thousands	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, 2013	$ 2,071,462	$ 8,586	$ 1,033	$ 143,766	$ 1,943,345	$ (25,268)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	49,165	0	0	0	49,165	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	2,144,181	8,586	1,033	143,766	1,986,739	4,057
Beginning balance at Dec. 31, 2014	2,687,594	11,005	1,005	658,918	2,069,647	(52,981)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	111,680	0	0	0		0
Net current period other comprehensive income	1,822	0	0	0	0
Cash dividends	(7,206)	0	0	0	(7,206)	0
Ending balance at Jun. 30, 2015	$ 2,793,890	$ 11,005	$ 1,005	$ 658,918	$ 2,174,121	$ (51,159)