Commitments and contingencies Textual (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Other Commitments [Line Items]
Operating Leases, Rent Expense	$ 2,000,000	$ 1,900,000	$ 3,800,000	$ 3,800,000
Cash Reserve Deposit Required and Made	7,100,000		7,100,000		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	$ 248,000	$ 502,000	$ 497,000