Organization and basis of presentation - Effect of new accounting pronouncement (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred leasing and financing costs, net		$ 0
Prepaid expenses and other assets	$ 1,822	1,126
Repurchase and loan agreements		763,369
Other secured borrowings	$ 160,392	502,599
As Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred leasing and financing costs, net		7,886
Prepaid expenses and other assets		415
Repurchase and loan agreements		767,513
Other secured borrowings		505,630
Adjustments
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred leasing and financing costs, net		(7,886)
Prepaid expenses and other assets		711
Repurchase and loan agreements		(4,144)
Other secured borrowings		$ (3,031)