Stock-Based Compensation Plans - Market Stock Units (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Number of Market Stock Units
Outstanding on December 31, 2019 (in shares)	139,643
Granted (in shares)	21,648
Exchanged for stock (in shares)	(24,035)
Outstanding on December 31, 2020 (in shares)	137,256	139,643
Maximum Shares Potentially Issuable
Outstanding on December 31, 2019 (in shares)	199,303
Granted (in shares)	32,472
Exchanged for stock (in shares)	(36,052)
Outstanding on December 31, 2020 (in shares)	195,723	199,303
MSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options expense	$ 0.7	$ 1.2
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Potential Shares From MSU Vest	0.00%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Potential Shares From MSU Vest	150.00%
Trading days	60 days