Long-term debt (Details) $ in Millions	1 Months Ended	6 Months Ended
	Jan. 31, 2020 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2020 CAD ($)	Mar. 18, 2020 USD ($)	Mar. 17, 2020 USD ($)	Jan. 31, 2020 CAD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2019 CAD ($)
Long-term debt
Less: unamortized discount		$ (4,700,000)					$ (5,800,000)
Less: unamortized deferred financing costs		(4,700,000)					(4,700,000)
Less: current maturities		(86,000,000.0)					(76,400,000)
Total long-term debt		420,100,000					473,500,000
Current maturities		(86,000,000.0)					(76,400,000)
Term loan maturity	2 years
Payments of Financing Costs		1,600,000
Shelf Registration authorized amount		$ 250,000,000
Availability of future shelf registration period		3 years
Senior secured term loans | APLP Holdings
Long-term debt
Minimum percentage of variable rate base	1.00%
Applicable margin (as a percent)	2.50%
Write-off of deferred financing costs	$ 500,000
Debt repriced						$ 380.0
Interest rate margin reduction due to repricing, as a percent	0.25%
Interest rate margin additional reduction due to repricing, as a percent	0.25%
Payments of Financing Costs		$ 700,000
Cadillac term loan, due 2025
Long-term debt
Debt service coverage ratio		1.20%
Debt service coverage ratio, consecutive term		4
Debt service coverage projected ratio		1.20%
Debt service coverage projected ratio, consecutive term		4
Revolver | APLP Holdings
Long-term debt
Line of Credit Facility, Amount Outstanding		$ 0
Borrowing capacity				$ 180,000,000	$ 200,000,000
Payments of Financing Costs		900,000
Letters of credit | APLP Holdings
Long-term debt
Line of Credit Facility, Amount Outstanding		$ 77,900,000
Maximum | Senior secured term loans | APLP Holdings
Long-term debt
Leverage ratio as defined in Credit Agreement						2.75
Maximum | Revolver | APLP Holdings
Long-term debt
Borrowing capacity				210,000,000
Upsizing borrowing capacity				$ 30,000,000
London Interbank Offered Rate (LIBOR) | Senior secured term loan facility, due 2025
Long-term debt
Minimum percentage of variable rate base		1.00%
Long-term debt excluding debentures | Senior secured term loan facility, due 2025
Long-term debt
Long-term Debt, Gross		$ 345,000,000.0					380,000,000.0
Current maturities		(83,000,000.0)					(72,500,000)
Long-term debt excluding debentures | Senior unsecured notes, due June 2036
Long-term debt
Long-term Debt, Gross		$ 154,100,000	$ 210.0				161,700,000	$ 210.0
Interest rate (as a percent)		5.95%	5.95%
Long-term debt excluding debentures | Cadillac term loan, due 2025
Long-term debt
Long-term Debt, Gross		$ 16,400,000					18,700,000
Current maturities		$ (3,000,000.0)					$ (3,900,000)
Long-term debt excluding debentures | London Interbank Offered Rate (LIBOR) | Senior secured term loan facility, due 2025
Long-term debt
Applicable margin (as a percent)		2.50%
Long-term debt excluding debentures | London Interbank Offered Rate (LIBOR) | Cadillac term loan, due 2025
Long-term debt
Applicable margin (as a percent)		1.61%