Junior Subordinated Interest Deferrable Debentures (Details 2) (USD $) In Thousands, unless otherwise specified			9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Trust VI	Sep. 30, 2013 Trust VII	Sep. 30, 2013 Trust VIII	Sep. 30, 2013 Trust IX	Sep. 30, 2013 Trust X	Sep. 30, 2013 Trust XI	Sep. 30, 2013 Trust XII
Junior subordinated deferrable interest debentures, major types of business trusts
Junior subordinated deferrable interest debentures	$ 190,726	$ 190,726	$ 25,774	$ 10,310	$ 25,774	$ 41,238	$ 34,021	$ 32,990	$ 20,619
Interest rate (as a percent)			3.71%	3.52%	3.32%	1.89%	1.92%	1.89%	1.71%
Interest rate index			LIBOR	LIBOR	LIBOR	LIBOR	LIBOR	LIBOR	LIBOR
Spread on interest rate index (as a percent)			3.45%	3.25%	3.05%	1.62%	1.65%	1.62%	1.45%