Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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Stock-Based Compensation Plans - 2007 Stock Incentive Plan (Details) - shares		1 Months Ended	12 Months Ended
	May 24, 2007	May 31, 2018	Dec. 31, 2019
Stock-based compensation plans
Number of shares available (in shares)			615,196
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 \| 2007 Stock Incentive Plan
Stock-based compensation plans
Number of shares awarded (in shares)			279,400
Equity Options \| 2007 Stock Incentive Plan
Stock-based compensation plans
Stock options outstanding (in shares)			0
Minimum \| Restricted Stock \| 2007 Stock Incentive Plan
Stock-based compensation plans
Vesting period	1 year
Minimum \| Restricted Stock \| 2018 Stock Incentive Plan
Stock-based compensation plans
Vesting period		1 year
Maximum \| Restricted Stock \| 2007 Stock Incentive Plan
Stock-based compensation plans
Vesting period	3 years
Maximum \| Restricted Stock \| 2018 Stock Incentive Plan
Stock-based compensation plans
Vesting period		3 years