Commitments and contingencies Textual (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Other Commitments [Line Items]
Operating Leases, Rent Expense	$ 2.0	$ 2.2
Cash Reserve Deposit Required and Made	$ 27.7		$ 31.8
Minimum [Member]
Other Commitments [Line Items]
Operating Leases, Lease Renewal Period Option	4 months
Maximum [Member]
Other Commitments [Line Items]
Operating Leases, Lease Renewal Period Option	10 years