Consolidated Statements Of Changes In Shareholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Common Class A [Member]	Common Class B [Member]	Common Stock [Member] Common Class A [Member]	Common Stock [Member] Common Class B [Member]	Surplus [Member]	Retained Earnings [Member]	Retained Earnings [Member] Common Class A [Member]	Retained Earnings [Member] Common Class B [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning Balance at Dec. 31, 2009	$ 1,559,115			$ 8,757	$ 1,678	$ 143,766	$ 1,429,863			$ (24,949)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustment resulting from adoption of a change in accounting for QSPEs and controlling financial interests effective January 1, 2010	4,904						4,904
Net income	193,044						193,044
Change in other comprehensive income, net of tax	(11,580)									(11,580)
Cash dividends	(12,521)						(12,521)
Ending Balance at Dec. 31, 2010	1,732,962			8,757	1,678	143,766	1,615,290			(36,529)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	195,028						195,028
Change in other comprehensive income, net of tax	(30,045)									(30,045)
Repurchase of shares (value)		(16,785)	(7,602)	(113)	(38)			(16,672)	(7,564)
Cash dividends	(12,430)						(12,430)
Ending Balance at Dec. 31, 2011	1,861,128			8,644	1,640	143,766	1,773,652			(66,574)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	134,348						134,348
Change in other comprehensive income, net of tax	(15,532)									(15,532)
Repurchase of shares (value)		(9,131)	(94,493)	(56)	(607)			(9,075)	(93,886)
Cash dividends	(12,313)						(12,313)
Ending Balance at Dec. 31, 2012	$ 1,864,007			$ 8,588	$ 1,033	$ 143,766	$ 1,792,726			$ (82,106)