Investments in Partnerships, Offshore Funds and Variable Interest Entities, Part I (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013 Entity	Sep. 30, 2012 Entity	Dec. 31, 2012 Entity	Dec. 31, 2011 Entity
Variable Interest Entity [Line Items]
Investments in affiliated entities	$ 84,300,000	$ 88,300,000	$ 83,900,000
Investments in unaffiliated entities	13,500,000	14,300,000	13,600,000
Investments in Partnerships by Accounting Method [Abstract]
Fair value	23,146,000	24,976,000	26,128,000
Equity Method Investments	74,606,000	77,628,000	71,421,000
Total	97,752,000	102,604,000	97,549,000
Maximum exposure to loss related to VIEs	9,900,000	8,200,000	7,700,000
Deferred carried interest in VIE	45,000	42,000	45,000
Total VIE assets	77,700,000	78,600,000	75,000,000
VIE [Member]
Entities Consolidated [Roll Forward]
Entities consolidated at beginning of period				1
Additional consolidated entities	0	0	0
Deconsolidated entities	0	0	0
Entities consolidated at end of period	1	1	1	1
Investments in Partnerships by Accounting Method [Abstract]
Total	13,782,000	23,086,000	18,507,000
VOE [Member]
Entities Consolidated [Roll Forward]
Entities consolidated at beginning of period				4
Additional consolidated entities	0	0	0
Deconsolidated entities	0	0	0
Entities consolidated at end of period	4	4	4	4
Prior to Consolidations [Member]
Investments in Partnerships by Accounting Method [Abstract]
Total	104,010,000	109,801,000	100,164,000
CFFs [Member]
Investments in Partnerships by Accounting Method [Abstract]
Total	3,253,000	1,540,000	5,388,000
CFFs [Member] | Affiliated [Member]
Investments in Partnerships by Accounting Method [Abstract]
Fair value	23,146,000	24,976,000	26,128,000
Equity Method Investments	0	0	0
Total	23,146,000	24,976,000	26,128,000
CFFs [Member] | VIE [Member]
Entities Consolidated [Roll Forward]
Entities consolidated at beginning of period				1
Additional consolidated entities	0	0	0
Deconsolidated entities	0	0	0
Entities consolidated at end of period	1	1	1	1
CFFs [Member] | VOE [Member]
Entities Consolidated [Roll Forward]
Entities consolidated at beginning of period				2
Additional consolidated entities	0	0	0
Deconsolidated entities	0	0	0
Entities consolidated at end of period	2	2	2	2
Partnerships [Member]
Investments in Partnerships by Accounting Method [Abstract]
Total	(9,511,000)	(8,737,000)	(8,003,000)
Partnerships [Member] | Affiliated [Member]
Investments in Partnerships by Accounting Method [Abstract]
Fair value	0	0	0
Equity Method Investments	26,717,000	32,475,000	28,158,000
Total	26,717,000	32,475,000	28,158,000
Partnerships [Member] | Unaffiliated [Member]
Investments in Partnerships by Accounting Method [Abstract]
Fair value	0	0	0
Equity Method Investments	6,080,000	7,518,000	6,505,000
Total	6,080,000	7,518,000	6,505,000
Partnerships [Member] | VIE [Member]
Entities Consolidated [Roll Forward]
Entities consolidated at beginning of period				0
Additional consolidated entities	0	0	0
Deconsolidated entities	0	0	0
Entities consolidated at end of period	0	0	0	0
Partnerships [Member] | VOE [Member]
Entities Consolidated [Roll Forward]
Entities consolidated at beginning of period				1
Additional consolidated entities	0	0	0
Deconsolidated entities	0	0	0
Entities consolidated at end of period	1	1	1	1
Offshore Funds [Member]
Investments in Partnerships by Accounting Method [Abstract]
Total	0	0	0
Offshore Funds [Member] | Affiliated [Member]
Investments in Partnerships by Accounting Method [Abstract]
Fair value	0	0	0
Equity Method Investments	34,460,000	30,901,000	29,679,000
Total	34,460,000	30,901,000	29,679,000
Offshore Funds [Member] | Unaffiliated [Member]
Investments in Partnerships by Accounting Method [Abstract]
Fair value	0	0	0
Equity Method Investments	7,349,000	6,734,000	7,079,000
Total	$ 7,349,000	$ 6,734,000	$ 7,079,000
Offshore Funds [Member] | VIE [Member]
Entities Consolidated [Roll Forward]
Entities consolidated at beginning of period				0
Additional consolidated entities	0	0	0
Deconsolidated entities	0	0	0
Entities consolidated at end of period	0	0	0	0
Offshore Funds [Member] | VOE [Member]
Entities Consolidated [Roll Forward]
Entities consolidated at beginning of period				1
Additional consolidated entities	0	0	0
Deconsolidated entities	0	0	0
Entities consolidated at end of period	1	1	1	1