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Employee Stock Purchase Plan (ESPP), Expense

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Exercise price of purchasing rights under CSPP as percentage of fair market value immediately prior to acquisition in case of acquisition by merger or sale.

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Percentage of voting interests to be acquired for business combination minimum.

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Period for shares issuance following the departure of director.

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Share Based Compensation Arrangement By Share Based Payment Award Award Restricted Stock Units Vesting Period Maximum.

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No definition available.

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Share Based Compensation Arrangement by Share Based Payment Award Award Restricted Stock Units Vesting Period Minimum.

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Share-Based Compensation.

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

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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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- Definition

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

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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

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 additional shares authorized for issuance under share-based payment arrangement.

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

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- Definition

Per share weighted-average price paid for shares purchased on open market for issuance under share-based payment arrangement.

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- Definition

Intrinsic value of vested award under share-based payment arrangement. Excludes share and unit options.

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No definition available.

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

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Share-Based Compensation (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		12 Months Ended
	May 21, 2015	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2012	May 31, 2011
Share-Based Compensation [Abstract]
Unrecognized stock-based compensation expense		$ 21.2
Number of years expected to recognize stock-based compensation		17 months
Share-based payment arrangement, expense		$ 28.0	$ 31.0	$ 28.0
Share-based compensation arrangement by Share-based payment award, number of shares authorized (in shares)		10.5
Share-based compensation arrangement by share-based payment award, number of additional shares authorized (in shares)	7.5
CSPP offering period		6 months
Shares issued following the director's departure from the board		six months and one day
Outstanding voting securities		50.00%
Exercise price of purchasing rights as percentage of fair market value per share in case of acquisition		85.00%
Incentive Compensation Plan 2011
Share-Based Compensation [Abstract]
Share-based compensation arrangement by Share-based payment award, number of shares authorized (in shares)					15.0
Restricted Stock Unit Activity Under 2011 Plan
Share-Based Compensation [Abstract]
unvested restricted stock units (in shares)		2.1	2.0
Restricted stock unit activity granted, weighted average grant date fair value (in dollars per share)		$ 17.96	$ 17.27	$ 20.62
Crewmember Stock Purchase Plan 2011
Share-Based Compensation [Abstract]
Share-based compensation arrangement by Share-based payment award, number of shares authorized (in shares)		17.5				8.0
Employees contribution towards purchase of common stock		10.00%
Purchase price discount based upon the stock price		15.00%
Employee stock purchase plan (ESPP), expense		$ 6.0	$ 9.0	$ 9.0
Stock issued under crewmember stock purchase plan (in shares)		4.1	3.2	3.2
Share-based compensation arrangement by share-based payment award, per share weighted average price of shares purchased (in dollars per share)		$ 8.94	$ 16.06	$ 15.21
Restricted Stock Units (RSUs)
Share-Based Compensation [Abstract]
unvested restricted stock units (in shares)		2.4
Share-based compensation aggregate intrinsic value, vested		$ 18.0	$ 15.0	$ 16.0
Restricted Stock Units (RSUs) \| Restricted Stock Unit Activity Under 2011 Plan
Share-Based Compensation [Abstract]
Share-based compensation arrangement by Share-based payment award, award vesting period		3 years
Deferred Stock Units (DSU's)
Share-Based Compensation [Abstract]
Minimum vesting period		1 year
Maximum vesting period		3 years
Crewmember Stock Purchase Plan 2011
Share-Based Compensation [Abstract]
Share-based compensation arrangement by share-based payment award, number of additional shares authorized (in shares)	15.0