Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Securities held to maturity-fair value	$ 6,588,874	$ 6,503,627
Securities available for sale-amortized cost	2,656,308	2,568,512
Mortgage loans-allowance for possible losses	$ 650	$ 650
Common Class A [Member]
STOCKHOLDERS’ EQUITY:
Common stock, par value	$ 1	$ 1
Common stock, shares authorized	7,500,000	7,500,000
Common stock, shares issued	3,434,763	3,434,763
Common stock, shares outstanding	3,434,763	3,434,766
Common Class B [Member]
STOCKHOLDERS’ EQUITY:
Common stock, par value	$ 1	$ 1
Common stock, shares authorized	200,000	200,000
Common stock, shares issued	200,000	200,000
Common stock, shares outstanding	200,000	200,000