Carrying amount as of the balance sheet date of obligations due all related parties.

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Summary of Significant Accounting Policies - Related Parties (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Investor \| Aerojet Rocketdyne Inc \| Blackrock, Inc.
Related Party Transaction [Line Items]
Ownership interest (percent)	15.00%	15.00%
Investor \| Aerojet Rocketdyne Inc \| Vanguard Group, Inc
Related Party Transaction [Line Items]
Ownership interest (percent)	10.00%	11.00%
Investor \| Gamco Investors, Inc. \| Aerojet Rocketdyne Inc
Related Party Transaction [Line Items]
Ownership interest (percent)	8.00%	9.00%
Aircraft for business travel \| Beneficial owner
Related Party Transaction [Line Items]
Expenses from transactions with related party	$ 0.1	$ 1.1	$ 0.6
Payable due to related party	0.1	0.1
Purchases of raw materials \| Beneficial owner
Related Party Transaction [Line Items]
Purchases from related party		0.3	0.3
Investment management fees \| Investor \| Gamco Investors, Inc.
Related Party Transaction [Line Items]
Expenses from transactions with related party	$ 0.8	$ 1.0	1.7
Lease commissions \| Investor \| CBRE
Related Party Transaction [Line Items]
Expenses from transactions with related party			$ 0.4