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Equity Incentive Plans and Stock-Based Compensation (Details 3) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Employee Stock Option [Member]
Stock-Based Compensation
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures	551,479	458,426
Share Based Compensation Arrangement by Share Based Payment Award Options, Grants in Period, Total Fair Value	$ 2.3	$ 1.9
Valuation assumptions
Expected stock price volatility (as a percent)	29.00%	32.00%
Risk free interest rate	2.60%	1.90%
Expected term	5 years 9 months 11 days	5 years 4 months 24 days
Weighted-average fair value of stock options granted (in dollars per share)	$ 4.24	$ 4.14
Restricted Stock and Stock Units [Member]
Nonvested equity stock and stock units
Nonvested at the beginning of the period (in shares)	5,861,349
Granted (in shares)	2,076,197	2,039,808
Vested (in shares)	(1,053,853)
Forfeited (in shares)	(251,943)
Nonvested at the end of the period (in shares)	6,631,750
Weighted-Average Grant-Date Fair Value
Nonvested at the beginning of the period (in dollars per share)	$ 12.68
Granted (in dollars per share)	12.91
Vested (in dollars per share)	11.96
Forfeited (in dollars per share)	12.87
Nonvested at the end of the period (in dollars per share)	$ 12.86

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Represents the total fair value of options for granted during the period.

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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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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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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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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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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Net number of share options (or share units) granted during the period.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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