Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Securities held to maturity-fair value	$ 7,470,133	$ 7,175,443
Securities available for sale-amortized cost	2,687,568	2,590,074
Mortgage loans-allowance for possible losses	$ 650	$ 650
Common Class A [Member]
STOCKHOLDERS’ EQUITY:
Common stock, par value	$ 1.00	$ 1
Common stock, shares authorized	7,500,000	7,500,000
Common stock, shares issued	3,436,166	3,436,166
Common stock, shares outstanding	3,436,166	3,436,166
Common Class B [Member]
STOCKHOLDERS’ EQUITY:
Common stock, par value	$ 1.00	$ 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