Commitments and Contingencies - Legal Proceedings and Other (Details)	12 Months Ended
	Dec. 31, 2017 USD ($)
Venture Capital Funds [Member]
Other [Abstract]
Committed total required invest funding	$ 35,000,000
Real Estate Fund [Member]
Other [Abstract]
Committed total required invest funding	25,000,000
Commitment agreement fundings	22,400,000
Real Estate Fund II [Member]
Other [Abstract]
Committed total required invest funding	28,000,000
Commitment agreement fundings	10,400,000
Oil and gas fund [Member]
Other [Abstract]
Committed total required invest funding	8,000,000
Commitment agreement fundings	$ 6,200,000