Commitments and contingencies Textual (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Other Commitments [Line Items]
Operating Leases, Rent Expense	$ 1,900,000
Cash Reserve Deposit Required and Made	25,700,000		33,000,000
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	$ 168,000	$ 251,000