Investments - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended
	Jun. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2010
Schedule of Investments [Line Items]
Equity Method Investment		$ 68,733,000		$ 68,733,000		$ 76,581,000
Marketable Securities		42,403,000		42,403,000		37,985,000
Unfunded commitments for capital contributions		8,458,000		8,458,000
Net realized and unrealized gains (losses) on private equity fund investments, including performance fees		1,933,000	$ 1,671,000	3,259,000	$ 5,633,000
Previously received carried interest subject to repayment		0		0
Limited partnership investment		2,635,000		2,635,000		4,014,000
Cost Method Investments		1,079,000		1,079,000
Contingent consideration	$ 7,916,000
Income (loss) from equity method investments		929,000	1,102,000	4,034,000	3,381,000
Amortization of intangible assets		621,000	647,000	1,863,000	1,941,000
Variable Interest Entity, Primary Beneficiary [Member]
Schedule of Investments [Line Items]
Consolidated assets		31,853,000		31,853,000		10,487,000
Consolidated liabilities		9,181,000		9,181,000		7,487,000
EMCP II [Member]
Schedule of Investments [Line Items]
Distribution Made to Limited Partner, Cash Distributions Paid				3,194,000
Trilantic IV [Member]
Schedule of Investments [Line Items]
Distribution Made to Limited Partner, Cash Distributions Paid				1,650,000
EMP III [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Schedule of Investments [Line Items]
Consolidated assets		7,024,000		7,024,000		7,327,000
Consolidated liabilities		153,000		153,000		75,000
Trilantic [Member]
Schedule of Investments [Line Items]
Issued LP Units (in shares)									500,000
Limited partnership investment									$ 16,090,000
G5 Evercore [Member]
Schedule of Investments [Line Items]
Equity Method Investment		$ 28,064,000		$ 28,064,000		32,756,000
Equity interest issued or issuable (in shares)	131,000
Equity interest issued or issuable, value	$ 7,232,000
Equity method investment (as a percent)		49.00%		49.00%
Income (loss) from equity method investments		$ (388,000)	(25,000)	$ 263,000	(45,000)
ABS [Member]
Schedule of Investments [Line Items]
Equity Method Investment		$ 40,669,000		$ 40,669,000		43,825,000
Equity method investment (as a percent)		45.00%		45.00%
Income (loss) from equity method investments		$ 1,317,000	$ 1,127,000	$ 3,771,000	$ 3,426,000
ECP II [Member]
Schedule of Investments [Line Items]
Distribution Made to Limited Partner, Cash Distributions Paid				3,000,000
CSI Capital [Member]
Schedule of Investments [Line Items]
Distribution Made to Limited Partner, Cash Distributions Paid				$ 2,909,000
Minimum [Member] | ECP II [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Schedule of Investments [Line Items]
Percent ownership of carried interest				8.00%
Maximum [Member] | ECP II [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Schedule of Investments [Line Items]
Percent ownership of carried interest				9.00%
EMCP III [Member]
Schedule of Investments [Line Items]
Subscribed capital commitments							$ 201,000,000
EMCP III [Member] | EMP III [Member]
Schedule of Investments [Line Items]
Capital commitment							10,750,000
Unfunded commitments for capital contributions		4,581,000		$ 4,581,000
EMCP III [Member] | Parent [Member]
Schedule of Investments [Line Items]
Capital commitment							1,000,000
Unfunded commitments for capital contributions		384,000		384,000
EMCP III [Member] | Noncontrolling Interest [Member]
Schedule of Investments [Line Items]
Capital commitment							9,750,000
Trilantic [Member]
Schedule of Investments [Line Items]
Investment		13,416,000		13,416,000		13,455,000
Trilantic [Member] | Trilantic IV [Member]
Schedule of Investments [Line Items]
Investment		3,000		3,000			29,000	$ 1,091,000
Trilantic [Member] | Trilantic V [Member]
Schedule of Investments [Line Items]
Capital commitment		5,000,000		5,000,000
Unfunded commitments for capital contributions		3,549,000		3,549,000
Investment		36,000		36,000		689,000	$ 825,000
Private Equity Funds [Member]
Schedule of Investments [Line Items]
Equity Method Investment		28,056,000		28,056,000		36,551,000
Private Equity Funds [Member] | ECP II [Member]
Schedule of Investments [Line Items]
Equity Method Investment		1,017,000		1,017,000		4,043,000
Cash		761,000		761,000
Escrow Deposit		78,000		78,000
Seller Note		66,000		66,000
Marketable Securities		112,000		112,000
Private Equity Funds [Member] | EMCP III [Member]
Schedule of Investments [Line Items]
Equity Method Investment		6,791,000		6,791,000		7,272,000
Private Equity Funds [Member] | Trilantic V [Member]
Schedule of Investments [Line Items]
Equity Method Investment		$ 2,957,000		$ 2,957,000		$ 2,911,000