Accounting Policies (Details) - USD ($)		12 Months Ended
	Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses	$ 0
Retained earnings		$ 279,800,000			$ 316,680,000
Concentration Risk [Line Items]
Credit loss (recoveries)		$ 3,000,000.0	$ (100,000)	$ 1,100,000
Cumulative Effect, Period Of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings	$ 0
Credit Concentration Risk | Accounts Receivable
Concentration Risk [Line Items]
Percentage of concentration risk	1.00%