Commitments and contingencies Textual (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Dec. 31, 2015
Other Commitments [Line Items]
Operating Leases, Rent Expense	$ 2.1	$ 2.0	$ 4.3	$ 3.9
Cash Reserve Deposit Required and Made	$ 27.2		$ 27.2	$ 21.7
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