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Stock-Based Compensation Plans - 2007 Stock Incentive Plan (Details) - shares	12 Months Ended
	Dec. 31, 2020	May 31, 2018	May 31, 2007
2007 Stock Incentive Plan
Stock-based compensation plans
Number of shares authorized (in shares)			2,800,000
2018 Stock Incentive Plan
Stock-based compensation plans
Number of shares authorized (in shares)		800,000
Restricted Stock \| 2018 Stock Incentive Plan
Stock-based compensation plans
Number of shares awarded (in shares)	598,750
Number of shares available (in shares)	295,846
Equity Options \| 2007 Stock Incentive Plan
Stock-based compensation plans
Stock options outstanding (in shares)	0
Minimum \| 2007 Stock Incentive Plan
Stock-based compensation plans
Vesting period	1 year
Minimum \| 2018 Stock Incentive Plan
Stock-based compensation plans
Vesting period	1 year
Maximum \| 2007 Stock Incentive Plan
Stock-based compensation plans
Vesting period	4 years
Maximum \| 2018 Stock Incentive Plan
Stock-based compensation plans
Vesting period	4 years