Stock-Based Compensation Plans - Stock Performance Rights (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Valuation assumptions:
Cash paid out for SPR excercises	$ 500,000	$ 13,400,000
Liability reflecting estimated fair value of future pay-outs	$ 14,437,000	14,908,000
Stock Performance Rights
Stock Performance Rights
Weighted average estimated value of SPRs outstanding (in USD per share)	$ 26.88
Valuation assumptions:
Expected volatility, minimum, percent	46.50%
Expected volatility, maximum, percent	66.90%
Risk-free rate of return, minimum	0.10%
Risk-free rate of return, maximum	0.20%
Expected annual dividend	$ 0
Stock options expense		$ 14,900,000
Liability reflecting estimated fair value of future pay-outs	$ 14,400,000
Number of SPRs
Outstanding on December 31, 2019 (in shares)	599,861
Exercised (in shares)	(18,861)
Outstanding on December 31, 2020 (in shares)	581,000	599,861
Exercisable on December 31, 2020 (in shares)	573,086
Weighted Average Exercise Price
Outstanding on December 31, 2019 (in USD per share)	$ 26.88	$ 26.56
Exercised (in USD per share)		16.48
Outstanding on December 31, 2020 (in USD per share)		26.88
Exercisable on December 31, 2020 (in USD per share)		$ 26.72
SPRs outstanding, intrinsic value	$ 14,600,000
Total unrecognized compensation cost	$ 200,000
Unrecognized cost, period for recognition (in years)	1 year
Shares vested (in shares)	43,397
Vested in period, fair value	$ 1,300,000
Weighted average remaining contractual term, SPRs outstanding (in years)	2 years
Weighted average remaining contractual term, SPRs exercisable (in years)	1.8 years
Stock Performance Rights | Minimum
Stock Performance Rights
Expiration period (in years)	7 years
Award vesting period (in years)	1 year
Valuation assumptions:
Expected term (in years)	6 months
Stock Performance Rights | Maximum
Stock Performance Rights
Award vesting period (in years)	3 years
Valuation assumptions:
Expected term (in years)	3 years 6 months