Investments - Carrying Value of Investments in Merchant Banking Funds (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Investments in and Advances to Affiliates [Line Items]
Investments in merchant banking funds	$ 16,772	$ 41,642
GCPE
Investments in and Advances to Affiliates [Line Items]
Investments in merchant banking funds	0	23,951
GCP I [Member]
Investments in and Advances to Affiliates [Line Items]
Investments in merchant banking funds	2,247	2,552
GCP II
Investments in and Advances to Affiliates [Line Items]
Investments in merchant banking funds	11,173	1,609
GCP II subject to Put Options
Investments in and Advances to Affiliates [Line Items]
Investments in merchant banking funds	0	10,520
GCP III [Member]
Investments in and Advances to Affiliates [Line Items]
Investments in merchant banking funds	1,367	903
Other Merchant Banking Funds
Investments in and Advances to Affiliates [Line Items]
Investments in merchant banking funds	$ 1,985	$ 2,107