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, 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	111,680	0
Net current period other comprehensive income	1,822	0	0	0	0	1,822
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)
Beginning balance at Dec. 31, 2015	2,872,109	11,005	1,005	658,918	2,265,621	(64,440)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	121,388	0	0	0		0
Net current period other comprehensive income	49,413	0	0	0	0	49,413
Cash dividends	(7,206)	0	0	0	(7,206)	0
Ending balance at Jun. 30, 2016	$ 3,035,704	$ 11,005	$ 1,005	$ 658,918	$ 2,379,803	$ (15,027)