Investments - Carrying Value of Investments in Merchant Banking Funds (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Investments in and Advances to Affiliates [Line Items]
Investments in merchant banking funds	$ 12,997	$ 16,772
GCP II [Member]
Investments in and Advances to Affiliates [Line Items]
Investments in merchant banking funds	7,516	11,173
GCP III [Member]
Investments in and Advances to Affiliates [Line Items]
Investments in merchant banking funds	2,025	1,367
GCP I [Member]
Investments in and Advances to Affiliates [Line Items]
Investments in merchant banking funds	1,587	2,247
Other Merchant Banking Funds
Investments in and Advances to Affiliates [Line Items]
Investments in merchant banking funds	$ 1,869	$ 1,985