Variable Interest Entities (Details)	3 Months Ended
	Mar. 31, 2018 USD ($) item	Dec. 31, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Variable Interest Entities
Loan loss reserves related to VIEs	$ 63,108,000	$ 62,783,000	$ 83,016,000	$ 83,712,000
Assets:
Restricted cash	131,659,000	139,398,000
Loans and investments, net	2,702,097,000	2,579,127,000
Other assets	69,258,000	62,264,000
Total assets	3,748,768,000	3,625,945,000
Liabilities:
Collateralized loan obligations	1,419,838,000	1,418,422,000
Debt fund	68,176,000	68,084,000
Other liabilities	77,881,000	99,813,000
Total liabilities	2,860,898,000	2,761,389,000
Consolidated VIEs | CLOs
Assets:
Restricted cash	130,656,000	138,736,000
Loans and investments, net	1,838,860,000	1,836,744,000
Other assets	15,211,000	14,011,000
Total assets	1,984,727,000	1,989,491,000
Liabilities:
Collateralized loan obligations	1,419,838,000	1,418,422,000
Debt fund	68,176,000	68,084,000
Other liabilities	3,187,000	2,046,000
Total liabilities	$ 1,491,201,000	$ 1,488,552,000
Unconsolidated VIEs
Variable Interest Entities
Number of VIEs where the reporting entity is not VIE's primary beneficiary and VIEs have variable interest | item	22
Carrying Amount	$ 397,880
Carrying amount of loans and investments before reserves related to VIEs	162,200,000
Loan loss reserves related to VIEs	61,400,000
Exposure to real estate debt	2,640,000,000
Unconsolidated VIEs | Loans
Variable Interest Entities
Carrying Amount	355,086,000
Unconsolidated VIEs | B Piece bonds
Variable Interest Entities
Carrying Amount	36,764,000
Unconsolidated VIEs | Agency interest only strips
Variable Interest Entities
Carrying Amount	3,862,000
Unconsolidated VIEs | Equity investments
Variable Interest Entities
Carrying Amount	$ 2,168,000