Earnings Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Basic:
Net income attributable to GAMCO Investors, Inc.'s shareholders	$ 116,853	$ 75,539	$ 69,682
Weighted average shares outstanding (in shares)	25,653	26,283	26,636
Basic net income attributable to GAMCO Investors, Inc.'s shareholders per share (in dollars per share)	$ 4.56	$ 2.87	$ 2.62
Diluted:
Net income attributable to GAMCO Investors, Inc.'s shareholders	$ 116,853	$ 75,539	$ 69,682
Weighted average shares outstanding (in shares)	25,653	26,283	26,636
Dilutive stock options and restricted stock awards (in shares)	59	153	88
Total (in shares)	25,712	26,436	26,724
Diluted net income attributable to GAMCO Investors, Inc.'s shareholders per share (in dollars per share)	$ 4.54	$ 2.86	$ 2.61