Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Basic:
Net income attributable to GAMCO Investors, Inc.'s shareholders	$ 27,893	$ 15,105	$ 50,438	$ 38,941
Weighted average shares outstanding (in shares)	25,679	26,258	25,710	26,338
Basic net income attributable to GAMCO Investors, Inc.'s shareholders per share (in dollars per share)	$ 1.09	$ 0.58	$ 1.96	$ 1.48
Diluted:
Net income attributable to GAMCO Investors, Inc.'s shareholders	$ 27,893	$ 15,105	$ 50,438	$ 38,941
Weighted average shares outstanding (in shares)	25,679	26,258	25,710	26,338
Dilutive stock options and restricted stock awards (in shares)	10	168	13	163
Total (in shares)	25,689	26,426	25,723	26,501
Diluted net income attributable to GAMCO Investors, Inc.'s shareholders per share (in dollars per share)	$ 1.09	$ 0.57	$ 1.96	$ 1.47