Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Basic [Abstract]
Income from continuing operations	$ 27,543	$ 23,775	$ 53,568	$ 46,923
Income from discontinued operations, net of taxes	0	326	0	1,954
Net income attributable to GAMCO Investors, Inc.'s shareholders	$ 27,543	$ 24,101	$ 53,568	$ 48,877
Weighted average shares outstanding (in shares)	29,234	25,065	29,241	25,098
Basic net income per share attributable to GAMCO Investors, Inc.'s shareholders [Abstract]
Continuing operations (in dollars per share)	$ 0.94	$ 0.95	$ 1.83	$ 1.87
Discontinued operations (in dollars per share)	0	0.01	0	0.08
Basic - Total (in dollars per share)	$ 0.94	$ 0.96	$ 1.83	$ 1.95
Diluted [Abstract]
Income from continuing operations	$ 27,543	$ 23,775	$ 53,568	$ 46,923
Income from discontinued operations, net of taxes	0	326	0	1,954
Net income attributable to GAMCO Investors, Inc.'s shareholders	$ 27,543	$ 24,101	$ 53,568	$ 48,877
Weighted average shares outstanding (in shares)	29,234	25,065	29,241	25,098
Dilutive stock options and restricted stock awards (in shares)	288	293	269	288
Total (in shares)	29,522	25,358	29,510	25,386
Diluted net income per share attributable to GAMCO Investors, Inc.'s shareholders [Abstract]
Continuing operations (in dollars per share)	$ 0.93	$ 0.94	$ 1.82	$ 1.85
Discontinued operations (in dollars per share)	0	0.01	0	0.08
Diluted - Total (in dollars per share)	$ 0.93	$ 0.95	$ 1.82	$ 1.93