Secured and unsecured senior debt Repayment of secured note payable (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2016 USD ($) note_payable	Jun. 30, 2016 USD ($) note_payable	Jun. 30, 2015 USD ($)
Debt Instrument [Line Items]
Repayments of Secured Debt		$ 233,168	$ 10,075
Effective rate (as a percent)	3.52%	3.52%
Secured notes payable
Debt Instrument [Line Items]
Effective rate (as a percent)	3.46%	3.46%
Two Secured Notes Payable | Secured notes payable
Debt Instrument [Line Items]
Number of notes payable repaid | note_payable	2
Repayments of Secured Debt	$ 173,800
Effective rate (as a percent)	5.59%	5.59%
Five Secured Notes Payable | Secured notes payable
Debt Instrument [Line Items]
Number of notes payable repaid | note_payable		5
Repayments of Secured Debt		$ 231,000
Effective rate (as a percent)	5.29%	5.29%