Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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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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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Number of shares authorized for issuance under share-based payment arrangement.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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The maximum annual amount of contributions to employee stock purchase plan made by plan participants.

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Number of participants in executive nonqualified excess plan (the "excess plan")

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Percentage of company matching contribution to employee stock purchase plan.

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Percentage of interest paid by the company on participant purchase plan contributions until purchase is made.

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The maximum number of shares that can be awarded per participant per year under an employee share-based payment plan.

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Equity Compensation and Employee Benefit Plans (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity Compensation [Abstract]
Maximum shares of common stock	20,000,000
Maximum annual shares awarded to employee	500,000
Shares available for granting additional awards	6,707,107
Unrecognized compensation cost of non-vested equity compensation awards	$ 10,400,000
Unrecognized compensation cost of non-vested equity compensation awards expected to be recognized over a weighted average period (years)	1 year 9 months 18 days
Maximum annual stock purchase plan contributions by plan participants	$ 20,000
Percentage of company matching contribution to employee stock purchase plan	15.00%
Percentage of interest accrues on purchase plan contributions	5.25%
Number of participants in executive nonqualified excess plan	45
Intrinsic value of stock options exercised	$ 0	$ 136,000	$ 484,000
Restricted Stock
Equity Compensation [Abstract]
Fair value of awards vested	$ 5,400,000	4,000,000.0	3,100,000
Restricted Stock \| Minimum
Equity Compensation [Abstract]
Vesting period (months)	12 months
Restricted Stock \| Maximum
Equity Compensation [Abstract]
Vesting period (months)	60 months
Performance Shares
Equity Compensation [Abstract]
Vesting period (months)	36 months
Fair value of awards vested	$ 5,800,000	$ 1,200,000	$ 1,300,000