FINANCIAL INSTRUMENTS Fair Value Hierarchy- Additional Information (Details) - USD ($)		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		$ 6,961,000	$ 6,753,000	$ 6,961,000	$ 6,753,000	$ 6,861,000	$ 6,763,000	$ 6,573,000	$ 8,957,000
Private equity funds measured at net asset value (1)	[1]	13,689,000		13,689,000			12,658,000
Transfers out of Level 3		0		(1,768,000)	0
Transfers from Level 2 to Level 1 due to lock-up period restriction expiration		(1,348,000)		(1,348,000)			0
Total realized and unrealized gains (losses) and amortization included in earnings, net			180,000		335,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases				1,750,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales					(2,539,000)
Quoted prices in active markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers out of Level 3			0		0
Net investment income (loss)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total realized and unrealized gains (losses) and amortization included in earnings, net		0	0
Change in unrealized gains		100,000	200,000	200,000	1,700,000
Debt instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		834,000	642,000	834,000	642,000	776,000	654,000	586,000	505,000
Transfers out of Level 3				0
Total realized and unrealized gains (losses) and amortization included in earnings, net		58,000	56,000	180,000	137,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases				0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales					0
Private equity and limited partnerships (1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		6,127,000	6,111,000	6,127,000	6,111,000	$ 6,085,000	$ 6,109,000	$ 5,987,000	$ 8,452,000
Transfers out of Level 3				1,768,000
Total realized and unrealized gains (losses) and amortization included in earnings, net		42,000	124,000	36,000	198,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases				1,750,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales					(2,539,000)
Private equity and limited partnerships (1) | Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers out of Level 3				1,800,000
Equity Securities [Member] | Quoted prices in active markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers out of Level 3		0		0
Transfers into Level 3		0	0	0	0
Equity Securities [Member] | Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers out of Level 3			0		0
Financial contracts receivable | Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers out of Level 3		0	0	0	0
Transfers into Level 3		0	0	0	0
Financial contracts payable
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings		100,000		216,000
Financial contracts payable | Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers out of Level 3			0		0
Transfers into Level 3		$ 0	$ 0	$ 0	$ 0

[1] Investments measured at fair value using the net asset value practical expedient have not been classified in the fair value hierarchy. The fair value amounts are presented in the above table to facilitate reconciliation to the condensed consolidated balance sheets.