Share and Unit-based Plans - Directors' Phantom Stock Plan (Details)	12 Months Ended
	Dec. 31, 2020 $ / shares shares	Dec. 31, 2019 $ / shares shares	Dec. 31, 2018 $ / shares shares
Phantom stock units
Share and unit-based plans [Line Items]
Number of common shares into which units can be converted (in shares)	1
Units
Balance at beginning of year (in shares)	7,216	0	4,054
Granted (in shares)	24,576	23,690	10,380
Vested (in shares)	(27,130)	(16,474)	(12,193)
Forfeited (in shares)	0	0	(2,241)
Balance at end of year (in shares)	4,662	7,216	0
Weighted Average Grant Date Fair Value
Balance at beginning of year (in dollars per share) | $ / shares	$ 43.29	$ 0	$ 79.82
Granted (in dollars per share) | $ / shares	17.11	40.26	49.55
Vested (in dollars per share) | $ / shares	20.94	38.94	54.40
Forfeited (in dollars per share) | $ / shares	0	0	77.91
Balance at end of year (in dollars per share) | $ / shares	$ 35.35	$ 43.29	$ 0
Director's Phantom Stock Plan
Share and unit-based plans [Line Items]
Deferral period for grant of units (in years)	3 years
Number of common shares into which units can be converted (in shares)	1
Maximum shares authorized under plan (in shares)	500,000
Shares available for issuance under plan (in shares)	110,062