Investments - Carrying Value of Investments in Merchant Banking Funds (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Investments in and Advances to Affiliates [Line Items]
Investments in merchant banking funds	$ 16,586	$ 16,772
GCP II
Investments in and Advances to Affiliates [Line Items]
Investments in merchant banking funds	10,988	11,173
GCP III [Member]
Investments in and Advances to Affiliates [Line Items]
Investments in merchant banking funds	1,367	1,367
GCP I [Member]
Investments in and Advances to Affiliates [Line Items]
Investments in merchant banking funds	2,246	2,247
Other Merchant Banking Funds
Investments in and Advances to Affiliates [Line Items]
Investments in merchant banking funds	$ 1,985	$ 1,985