Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Available-for-sale Securities, Amortized Cost Basis	$ 5,192,419	$ 4,029,858
Held-to-maturity Securities, Fair Value Disclosure	$ 1,448	$ 1,980
Class A Common Stock [Member]
Common stock, par value	$ 1	$ 1
Common stock, shares issued (shares)	11,000,000	11,000,000
Common stock, shares outstanding (shares)	8,588,031	8,644,307
Class B Common Stock [Member]
Common stock, par value	$ 1	$ 1
Common stock, shares issued (shares)	2,000,000	2,000,000
Common stock, shares outstanding (shares)	1,032,883	1,639,812