Summary of Significant Accounting Policies - Noncontrolling interest (Details) $ in Millions	Dec. 31, 2021 USD ($)
Related parties
Noncontrolling Interest [Line Items]
Cumulative contributions from noncontrolling interest owner	$ 3.8
VOLT
Noncontrolling Interest [Line Items]
Cumulative contributions from controlling interest owner	$ 11.9
VOLT
Noncontrolling Interest [Line Items]
Controlling interest (as a percent)	76.00%
VOLT | Related parties
Noncontrolling Interest [Line Items]
Noncontrolling interest (as a percent)	24.00%