Debt (Details) - USD ($) $ in Thousands			1 Months Ended		12 Months Ended
	Aug. 08, 2019	Mar. 15, 2019	Jan. 31, 2015	Nov. 30, 2013	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Mar. 14, 2019	Jan. 31, 2018
Debt
Number of days before the maturity of the senior notes due November 2020 that the credit facility matures		91 days
Number of days before the maturity of the senior notes due November 2020, as amended or replaced, that the credit facility matures		91 days
Repayment of outstanding debt					$ 18,000
Available borrowing capacity					50,000
Interest expense					12,795	$ 12,377	$ 12,125
Amortization of debt issuance costs					$ 300	$ 300	$ 300
Revolving facility
Debt
Face amount of the debt									$ 25,000
Interest rate (as a percent)									4.20%
Maximum borrowing capacity		$ 50,000						$ 25,000
Repayment of outstanding debt	$ 18,000
7.5% Senior Unsecured Notes due November 2020
Debt
Face amount of the debt				$ 140,000
Interest rate (as a percent)				7.50%
Debt issuance costs incurred				$ 2,100
6.5% Senior Notes due November 2020
Debt
Face amount of the debt			$ 25,000
Interest rate (as a percent)			6.50%
Debt issuance costs incurred			$ 200