Consolidated Statements Of Changes In Shareholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Class A [Member]	Common Class B [Member]	Common Stock [Member]	Common Stock [Member] Common Class A [Member]	Common Stock [Member] Common Class B [Member]	Surplus [Member]	Surplus [Member] Common Class A [Member]	Surplus [Member] Common Class B [Member]	Retained Earnings [Member]	Retained Earnings [Member] Common Class A [Member]	Retained Earnings [Member] Common Class B [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Other Comprehensive Income (Loss) [Member] Common Class A [Member]	Accumulated Other Comprehensive Income (Loss) [Member] Common Class B [Member]
Beginning Balance at Dec. 31, 2008	$ 1,443,375				$ 8,757	$ 1,678	$ 143,766			$ 1,326,054			$ (36,880)
Comprehensive income:
Net income	116,331									116,331
Change in other comprehensive income, net of tax	11,931												11,931
Total comprehensive income	128,262
Cash dividends	(12,522)									(12,522)
Adjustment resulting from adoption of a change in accounting for QSPEs and controlling financial interests effective January 1, 2010	4,904									4,904
Ending Balance at Dec. 31, 2009	1,559,115				8,757	1,678	143,766			1,429,863			(24,949)
Comprehensive income:
Net income	193,044									193,044
Change in other comprehensive income, net of tax	(11,580)												(11,580)
Total comprehensive income	181,464
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)
Comprehensive income:
Net income	195,028									195,028
Change in other comprehensive income, net of tax	(30,045)												(30,045)
Total comprehensive income	164,983
Cash dividends	(12,430)									(12,430)
Repurchase of shares (value)		(16,785)	(7,602)								(16,672)	(7,564)
Repurchase of shares (shares)		(112,471)	(37,863)
Ending Balance at Dec. 31, 2011	$ 1,861,128				$ 8,644	$ 1,640	$ 143,766			$ 1,773,652			$ (66,574)