Commitments and contingencies Textual (Details) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Other Commitments [Line Items]
Operating Leases, Rent Expense	$ 2,200,000	$ 1,900,000
Cash Reserve Deposit Required and Made	$ 0		$ 21,700,000
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