Debt - Deferred Financing Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Financing costs	$ 24,446	$ 23,145
Less: accumulated amortization	(7,039)	(12,241)
Total deferred financing costs, net	17,407	10,904
Amortization of financing costs	4,700	5,000	$ 6,100
Revolving Credit Facility [Member] | Unsecured revolving credit facility [Member]
Debt Instrument [Line Items]
Net deferred financing costs	$ 8,300	$ 4,500