Consolidated Balance Sheets (Parenthetical) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Amortized cost	$ 495,931,000	$ 1,414,595,000
Held-to-maturity securities, fair value	$ 1,371,118,000	$ 281,924,000
Preferred stock, par value	$ 1.00	$ 1.00
Preferred stock, shares authorized	100,000	100,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Class A Common Stock [Member]
Common stock, par value	$ 1.00	$ 1.00
Common stock, shares authorized	10,000,000	10,000,000
Common stock, shares issued	3,578,404	3,568,079
Class B Common Stock [Member]
Common stock, par value	$ 1.00	$ 1.00
Common stock, shares authorized	5,000,000	5,000,000
Common stock, shares issued	1,978,180	1,986,880