Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Basic [Abstract]
Income from continuing operations	$ 26,025	$ 23,148
Income from discontinued operations, net of taxes	0	1,628
Net income attributable to GAMCO Investors, Inc.'s shareholders	$ 26,025	$ 24,776
Weighted average shares outstanding (in shares)	29,247	25,132
Basic net income per share attributable to GAMCO Investors, Inc.'s shareholders [Abstract]
Continuing operations (in dollars per share)	$ 0.89	$ 0.92
Discontinued operations (in dollars per share)	0	0.07
Basic - Total (in dollars per share)	$ 0.89	$ 0.99
Diluted [Abstract]
Income from continuing operations	$ 26,025	$ 23,148
Income from discontinued operations, net of taxes	0	1,628
Net income attributable to GAMCO Investors, Inc.'s shareholders	$ 26,025	$ 24,776
Weighted average shares outstanding (in shares)	29,247	25,132
Dilutive stock options and restricted stock awards (in shares)	437	282
Total (in shares)	29,684	25,414
Diluted net income per share attributable to GAMCO Investors, Inc.'s shareholders [Abstract]
Continuing operations (in dollars per share)	$ 0.88	$ 0.91
Discontinued operations (in dollars per share)	0	0.06
Diluted - Total (in dollars per share)	$ 0.88	$ 0.97