Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Basic:
Net income attributable to GAMCO Investors, Inc.'s shareholders	$ 23,665	$ 33,098	$ 80,569	$ 83,536
Weighted average shares outstanding (in shares)	25,296	25,625	25,385	25,682
Basic net income attributable to GAMCO Investors, Inc.'s shareholders per share (in dollars per share)	$ 0.94	$ 1.29	$ 3.17	$ 3.25
Diluted:
Net income attributable to GAMCO Investors, Inc.'s shareholders	$ 23,665	$ 33,098	$ 80,569	$ 83,536
Weighted average shares outstanding (in shares)	25,296	25,625	25,385	25,682
Dilutive stock options and restricted stock awards (in shares)	221	75	210	35
Total (in shares)	25,517	25,700	25,595	25,717
Diluted net income attributable to GAMCO Investors, Inc.'s shareholders per share (in dollars per share)	$ 0.93	$ 1.29	$ 3.15	$ 3.25