Risk Management and Use of Derivative Financial Instruments - Foreign Currency Derivatives Details (Details) € in Thousands, £ in Thousands, kr in Thousands, $ in Thousands	Mar. 31, 2020 USD ($) instrument	Mar. 31, 2020 NOK (kr) instrument	Mar. 31, 2020 EUR (€) instrument	Mar. 31, 2020 GBP (£) instrument
Derivative Disclosure
Fair value, foreign currency derivatives	$ 35,440
Derivatives Designated as Hedging Instruments | Designated as Cash Flow Hedging Instruments | Foreign currency collars | EUR
Derivative Disclosure
Derivative number of instruments | instrument	88	88	88	88
Notional Amount | €			€ 295,049
Fair value, foreign currency derivatives	$ 25,692
Derivatives Designated as Hedging Instruments | Designated as Cash Flow Hedging Instruments | Foreign currency collars | GBP
Derivative Disclosure
Derivative number of instruments | instrument	63	63	63	63
Notional Amount | £				£ 44,000
Fair value, foreign currency derivatives	$ 4,947
Derivatives Designated as Hedging Instruments | Designated as Cash Flow Hedging Instruments | Foreign currency collars | NOK
Derivative Disclosure
Derivative number of instruments | instrument	3	3	3	3
Notional Amount | kr		kr 2,000
Fair value, foreign currency derivatives	$ 42
Derivatives Designated as Hedging Instruments | Designated as Cash Flow Hedging Instruments | Foreign currency forward contracts | EUR
Derivative Disclosure
Derivative number of instruments | instrument	3	3	3	3
Notional Amount | €			€ 12,951
Fair value, foreign currency derivatives	$ 4,706
Derivatives Designated as Hedging Instruments | Derivatives in Net Investment Hedging Relationships | Foreign currency collars | NOK
Derivative Disclosure
Derivative number of instruments | instrument	1	1	1	1
Notional Amount | kr		kr 2,500
Fair value, foreign currency derivatives	$ 53