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Equity Incentive Plans and Stock-Based Compensation (Details 3) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Employee Stock Option [Member]
Stock-Based Compensation
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures	70,000	40,000	621,479	498,426
Share Based Compensation Arrangement by Share Based Payment Award Options, Grants in Period, Total Fair Value	$ 0.3	$ 0.2	$ 2.6	$ 2.1
Valuation assumptions
Expected stock price volatility (as a percent)	24.00%	32.00%		32.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate	2.74%	1.76%
Expected term	5 years 10 months 2 days	5 years 4 months 6 days	5 years 9 months 11 days
Weighted-average fair value of stock options granted (in dollars per share)	$ 3.94	$ 3.84	$ 4.21	$ 4.12
Weighted-Average Grant-Date Fair Value
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate, Minimum			2.60%	1.76%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate, Maximum			2.74%	1.93%
Employee Stock Purchase Plan
Stock-Based Compensation
Stock Issued During Period, Shares, Employee Stock Purchase Plans			297,497	361,994
Valuation assumptions
Expected stock price volatility (as a percent)			27.00%	27.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate			2.05%	0.98%
Expected term			6 months	6 months
Weighted-average fair value of stock options granted (in dollars per share)			$ 3.14	$ 2.87
Weighted-Average Grant-Date Fair Value
Employee Stock Purchase Plans, Weighted Average Price Per Share			$ 11.66	$ 10.33
Share Based Compensation Arrangement by Share Based Payment Award Additional Number of Shares Authorized			2,000,000
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)	326,106	151,354	2,402,303	2,191,162
Vested (in shares)			(1,127,011)
Forfeited (in shares)			(1,698,558)
Nonvested at the end of the period (in shares)	5,438,083		5,438,083
Weighted-Average Grant-Date Fair Value
Nonvested at the beginning of the period (in dollars per share)			$ 12.68
Granted (in dollars per share)			13.08
Vested (in dollars per share)			11.99
Forfeited (in dollars per share)			12.88
Nonvested at the end of the period (in dollars per share)	$ 12.95		$ 12.95
Minimum [Member] | Employee Stock Option [Member]
Valuation assumptions
Expected stock price volatility (as a percent)			23.73%
Expected term				5 years 4 months 6 days
Maximum [Member] | Employee Stock Option [Member]
Valuation assumptions
Expected stock price volatility (as a percent)			29.00%
Expected term				5 years 4 months 21 days

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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.

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

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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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