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Commitments and contingencies Textual (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Dec. 31, 2015
Other Commitments [Line Items]          
Operating Leases, Rent Expense $ 2,100 $ 2,055 $ 6,400 $ 6,100  
Cash Reserve Deposit Required and Made $ 0   $ 0   $ 21,700
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