Accounts Receivable Securitization (Details) - Line of Credit - Accounts Receivable Securitization Facility - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Short-term Debt [Line Items]
Maximum borrowing capacity	$ 100,000,000
Unused commitment fee (as a percent)	0.60%
Accounts receivable eligible for securitization	$ 41,282,000	$ 37,869,000
Outstanding borrowings	0	0
Letters of credit outstanding	41,211,000	52,536,000
Borrowings and issuance of letters of credit remaining capacity	71,000	0
Cash collateral		14,667,000
Costs associated with receivables facility	$ 1,441,000	2,593,000	$ 171,000
Minimum
Short-term Debt [Line Items]
Security facility program fee (as a percent)	2.00%
Maximum
Short-term Debt [Line Items]
Security facility program fee (as a percent)	2.50%
Restricted Cash
Short-term Debt [Line Items]
Cash collateral		$ 14,667,000