Summary of Significant Accounting Policies - Related Parties (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2016	Nov. 30, 2015	Nov. 30, 2014
Aircraft for Business Travel [Member] | SP Corporate
Related Party Transaction [Line Items]
Payments to related party		$ 0.9	$ 1.1
Payable due to related party	$ 0.7	$ 0.2
Steel Partners Holdings L.P. [Member]
Related Party Transaction [Line Items]
Percentage of ownership interest in subsidiary		100.00%
Gamco Investors, Inc. | Investor
Related Party Transaction [Line Items]
Percentage Of Ownership Interests	14.00%	12.00%
Investment management fee expenses for services received	$ 0.1	$ 1.1	$ 1.1	$ 1.2
Blackrock, Inc. | Investor
Related Party Transaction [Line Items]
Percentage Of Ownership Interests	9.00%	10.00%