Derivative Instruments - Schedule of settlement of fair value hedges (Details) (Fair value hedges, USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Notes payable and debt
Derivative [Line Items]
Cumulative reduction to interest expense	$ 15,926	$ 12,019
Remaining balance	5,698	9,605
Weighted average years remaining to maturity	1 year 6 months	2 years 6 months
Deposit liabilities
Derivative [Line Items]
Cumulative reduction to interest expense	25,588	11,070
Remaining balance	$ 207,607	$ 138,415
Weighted average years remaining to maturity	24 years 8 months 12 days	33 years