Long-Term Debt, Net - Additional Information (Details)		12 Months Ended
	Oct. 16, 2020 USD ($) SeriesNote	Dec. 31, 2020 USD ($) SeriesNote instrument	Dec. 31, 2019 USD ($)
Debt Instrument [Line Items]
Finance lease obligations		$ 0
Number of series of debt issued | SeriesNote	2	2
Maturity date		Jun. 19, 2023
Current borrowing capacity		$ 225,000,000
Line of credit facility reduced minimum borrowing capacity		$ 50,000,000
Basis spread on variable rate		1.50%
Performance bonds under credit facility		$ 12,900,000
Remaining borrowing capacity		101,100,000
Performance bonds		$ 6,100,000
Calculated covenant leverage ratio		2.82%
Calculated interest coverage ratio		6.09%
Professional service fees and expenses		$ 1,600,000
Total long-term debt		$ 261,000,000	$ 307,000,000
Interest Rate Swap [Member]
Debt Instrument [Line Items]
Derivative, number of instruments held | instrument		2
Derivative, notional amount		$ 50,000,000
LIBOR [Member]
Debt Instrument [Line Items]
LIBOR floor interest rate		0.50%
Maximum [Member]
Debt Instrument [Line Items]
Basis spread on variable rate		2.875%
2011 Seniors Notes [Member]
Debt Instrument [Line Items]
Face amount		$ 150,000,000
Senior Notes Series A [Member]
Debt Instrument [Line Items]
Face amount	$ 45,000,000	$ 75,000,000
Interest rate, effective percentage	4.09%	4.01%
Maturity date	Jan. 12, 2026	Sep. 30, 2021
Outstanding borrowings		$ 15,000,000
Total long-term debt		75,000,000
Senior Notes Series B [Member]
Debt Instrument [Line Items]
Face amount	$ 15,000,000	$ 75,000,000
Interest rate, effective percentage	4.38%	4.11%
Maturity date	Jan. 12, 2028	Sep. 30, 2023
Credit Facility [Member]
Debt Instrument [Line Items]
Interest coverage ratio, minimum		3.00%
Total long-term debt		$ 111,000,000	157,000,000
2020 Seniors Notes [Member]
Debt Instrument [Line Items]
Face amount	$ 60,000,000
Total long-term debt		$ 150,000,000	$ 150,000,000