Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Available-for-sale securities, amortized cost	$ 1,244,972	$ 903,556
Held-to-maturity securities, fair value	$ 184,822	$ 233,524
Common Class A [Member]
Common stock, par value	$ 1.00	$ 1.00
Common stock, shares authorized	10,000,000	10,000,000
Common stock, shares issued	3,548,317	3,528,867
Common Class B [Member]
Common stock, par value	$ 1.00	$ 1.00
Common stock, shares authorized	5,000,000	5,000,000
Common stock, shares issued	1,994,380	2,011,380