Commitments and contingencies Textual (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Other Commitments [Line Items]
Operating Leases, Rent Expense	$ 1,900,000	$ 1,900,000
Cash Reserve Deposit Required and Made	14,100,000		21,000,000
Minimum [Member]
Other Commitments [Line Items]
Operating Leases, Lease Renewal Period Option	1 year
Maximum [Member]
Other Commitments [Line Items]
Operating Leases, Lease Renewal Period Option	10 years
Affiliated Entity [Member]
Other Commitments [Line Items]
Operating Leases, Rent Expense	$ 251,000	$ 249,000