Commitments and contingencies (Other investment commitments) (Details) - USD ($) $ in Thousands	Dec. 30, 2015	Dec. 29, 2014	Sep. 30, 2016	Dec. 31, 2015
Fixed maturity commitment
Other Commitments [Line Items]
Remaining commitment			$ 29,595	$ 34,888
Loan Origination Commitments [Member]
Other Commitments [Line Items]
Capital commitment			25,000
Remaining commitment			0
Investment commitment
Other Commitments [Line Items]
Capital commitment			308,000	263,000
Remaining commitment			165,448	185,548
Fund A
Other Commitments [Line Items]
Remaining capital commitment			0	10,000
Total capital commitment	$ 20,000	$ 20,000
Fund B
Other Commitments [Line Items]
Remaining capital commitment			$ 0	$ 9,536
Total capital commitment	$ 25,000