Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Basic:
Net income attributable to GAMCO Investors, Inc.'s shareholders	$ 33,098	$ 19,004	$ 83,536	$ 57,945
Weighted average shares outstanding (in shares)	25,625	26,250	25,682	26,309
Basic net income attributable to GAMCO Investors, Inc.'s shareholders per share (in dollars per share)	$ 1.29	$ 0.72	$ 3.25	$ 2.20
Diluted:
Net income attributable to GAMCO Investors, Inc.'s shareholders	$ 33,098	$ 19,004	$ 83,536	$ 57,945
Weighted average shares outstanding (in shares)	25,625	26,250	25,682	26,309
Dilutive stock options and restricted stock awards (in shares)	75	189	35	171
Total (in shares)	25,700	26,439	25,717	26,480
Diluted net income attributable to GAMCO Investors, Inc.'s shareholders per share (in dollars per share)	$ 1.29	$ 0.72	$ 3.25	$ 2.19