Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Available-for-sale Securities, Amortized Cost Basis	$ 6,885,797	$ 7,163,574
Class A Common Stock
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, shared authorized	16,000,000	16,000,000
Common stock, shares issued	11,005,220	11,005,220
Common stock, shares outstanding	11,005,220	11,005,220
Class B Common Stock
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, shared authorized	2,000,000	2,000,000
Common stock, shares issued	1,005,185	1,005,185
Common stock, shares outstanding	1,005,185	1,005,185
Mortgage Backed Securities, Other
Available-for-sale Securities, Amortized Cost Basis	$ 4,692,447	$ 3,628,187
Held-to-maturity Securities, Fair Value	$ 265	$ 544