Commitments and contingencies Textual (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Other Commitments [Line Items]
Operating Leases, Rent Expense	$ 2,000,000	$ 2,000,000	$ 3,900,000	$ 3,800,000
Cash Reserve Deposit Required and Made	13,000,000		$ 13,000,000		$ 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	$ 0	$ 62,000	$ 0	$ 124,000