Debt Obligations - Bank Borrowings Terms (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Debt Obligations
Amount borrowed	$ 3,500,000	$ 40,500,000
Repayment amount	110,600,000
Bank Borrowings - Line of Credit
Debt Obligations
Maximum available under facility	$ 600,000,000
Additional extension period option	1 year
Unused commitment fee (as a percent)	0.35%
Amount borrowed	$ 3,500,000	$ 40,500,000
Repayment amount	$ 110,600,000
Bank Borrowings - Line of Credit | LIBOR
Debt Obligations
Basis spread over base rate (as a percent)	1.50%