Commitments and Contingencies (Unfunded Commitments) (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)
Other Commitments [Line Items]
Percentage of Capital Committed that May be Drawn Down	100.00%
Performance-Based Commitments	$ 530,143
Strategic Investments	9,322
Total	539,465
Loans and Other Lending Investments
Other Commitments [Line Items]
Performance-Based Commitments	505,345
Strategic Investments	0
Total	505,345
Real Estate
Other Commitments [Line Items]
Performance-Based Commitments	9,774
Strategic Investments	0
Total	9,774
Other Investments
Other Commitments [Line Items]
Performance-Based Commitments	15,024
Strategic Investments	9,322
Total	24,346
Loan participations, not the obligation of the Company
Other Commitments [Line Items]
Performance-Based Commitments	$ 35,100