Debt - ActivityRevolving Credit Facility (Details) - USD ($) $ in Thousands		1 Months Ended				9 Months Ended
	Aug. 10, 2020	Aug. 31, 2020	Oct. 31, 2019	Oct. 31, 2018	Aug. 31, 2016	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2018	Jun. 30, 2017	May 31, 2017
Debt instruments
Long-term debt						$ 34,028	$ 53,464
Current portion of long-term debt						9,136
Remaining amount available to borrow						0	0
Repayment of outstanding debt	$ 10,800		$ 28,900	$ 41,400		10,846
Revolving credit facility
Debt instruments
Maximum borrowing capacity			55,000	85,000	$ 150,000			$ 200,000
Additional borrowing capacity									$ 25,000	$ 25,000
Outstanding borrowings in long term debt						43,832	54,678
Repayment of outstanding debt		$ 10,800
Incurred deferred financing costs			$ 800	$ 900	$ 500
Unamortized deferred financing costs						700	1,200
Letter of credit
Debt instruments
Outstanding borrowings in long term debt						$ 300	$ 300