Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Estimated Forfeiture Rate

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- Definition

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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- Definition

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

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- Definition

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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- Definition

The cash inflow associated with the amount received from the stock plan during the period.

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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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- Definition

Discount rate from fair value on offering date that participants pay for shares.

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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- Definition

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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No definition available.

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- Definition

The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan.

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- Definition

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

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- Definition

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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- Definition

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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- Definition

Number of options outstanding, including both vested and non-vested options.

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- Definition

Purchase price of common stock expressed as a percentage of its fair value.

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- Definition

Number of shares issued during the period as a result of an employee stock purchase plan.

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Stock Options and Employee Stock Purchase Plan (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options outstanding (in shares)	430,250		430,250		475,601
Total intrinsic values of options exercised in period			$ 4,000	$ 3,000
Compensation cost recognized	$ 6,251	$ 6,530	$ 12,363	$ 12,843
Estimated forfeiture rates			12.22%	11.52%
Cash received upon the issuance of common stock			$ 4,232	$ 3,303
Share-based Payment Arrangement, Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost recognized	200	200	400	$ 400
Unrecognized compensation cost related to non-vested awards granted	5,300		$ 5,300		$ 5,800
Weighted-average period to recognize compensation cost (in years)			4 years 6 months
Restricted (Performance) Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)			73,094	82,112
Granted (in usd per share)			$ 94.40	$ 70.99
Restricted Stock And Restricted Stock Unit (RSU)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost recognized	5,400	5,700	$ 10,700	$ 11,300
Unrecognized compensation cost related to non-vested awards granted	$ 43,800		$ 43,800		$ 38,600
Restricted Stock And Restricted Stock Unit (RSU) \| Board of Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting periods			1 year
Restricted Stock And Restricted Stock Unit (RSU) \| Chief Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting periods			8 years
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stocks outstanding (in shares)	484,205		484,205		820,566
Weighted-average period to recognize compensation cost (in years)			3 years 10 months 24 days
Granted (in shares)			0
Granted (in usd per share)			$ 0
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average period to recognize compensation cost (in years)			4 years 3 months 18 days
Granted (in shares)			163,380
Minimum \| Restricted Stock And Restricted Stock Unit (RSU) \| Senior Staff
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting periods			4 years
Maximum \| Restricted Stock And Restricted Stock Unit (RSU) \| Senior Staff
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting periods			5 years
2007 Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum issuance of common stock (in shares)	4,500,000		4,500,000
Purchase price of common stock, percent			85.00%
Number of options outstanding (in shares)	7,250		7,250
Number of stocks outstanding (in shares)	0		0
2015 Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum issuance of common stock (in shares)	4,200,000		4,200,000
Number of options outstanding (in shares)	423,000		423,000
Number of stocks outstanding (in shares)	272,940		272,940
2015 Stock Option Plan \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Market value of common stock on the date of grant for incentive stock options			100.00%
Employee Stock Purchase Plan \| Common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum issuance of common stock (in shares)	2,000,000,000,000		2,000,000,000,000
Market value of common stock on the date of grant for incentive stock options			85.00%
Compensation cost recognized	$ 700	$ 600	$ 1,300	$ 1,100
Estimated forfeiture rates			11.15%	16.50%
Number of shares available for issuance (in shares)	0		0
Maximum earnings withheld by the employees	15.00%		15.00%
Issuance of shares under employee stock purchase plan (in shares)			58,145	53,694
Cash received upon the issuance of common stock			$ 4,200	$ 3,300