Percentage of MPS schools were not in academic jeopardy.

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The number of additional grants made during the period due to the outperform level 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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Represents the aggregate fair value of share-based compensation awards granted during the period using the disclosed option pricing methodology.

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Represents information pertaining to the number of days considered for computation of average closing prices of the company's stock to enable vesting of awards.

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Percentage of target award believed to be probable at the highest level of the target award.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Unrecognized cost of unvested share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

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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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Price of a single share of a number of saleable stocks of a company.

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Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

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Equity Incentive Plan - Other (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended			6 Months Ended		12 Months Ended
	Aug. 02, 2017	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2017	Sep. 30, 2017
Equity Transactions
Fair value of share-based compensation awards granted in period		$ 16.7		$ 13.3
Fair value of share-based compensation awards vested in period					$ 12.9	$ 6.0
Vested (in shares)					91,732
Vesting Performance
Equity Transactions
Number of consecutive days considered for the computation of average closing stock prices							30 days
Equity Incentive Market Based Restricted Stock Awards
Equity Transactions
Granted (in dollars per share)							$ 14.35
Equity Incentive Market Based Restricted Stock Awards \| Vesting Performance
Equity Transactions
Nonvested at the end of the period (in shares)		205,343			205,343
Equity Incentive Market Based Restricted Stock Awards \| Service based awards
Equity Transactions
Granted (in shares)					557,870
Vested (in shares)					424,153
Nonvested at the end of the period (in shares)		1,387,834			1,387,834
Equity Incentive Market Based Restricted Stock Awards \| Stock price performance target one
Equity Transactions
Stock price			$ 13				13
Vested (in shares)					10,000
Equity Incentive Market Based Restricted Stock Awards \| Stock price performance target two
Equity Transactions
Stock price			16				16
Equity Incentive Market Based Restricted Stock Awards \| Stock price performance target three
Equity Transactions
Stock price			$ 19				$ 19
Restricted Stock
Equity Transactions
Stock based compensation expense		$ 3.9		4.2	$ 7.8	8.2
Unrecognized compensation		$ 22.0			$ 22.0
Weighted average period for recognition of total unrecognized compensation expense related to unvested stock options granted					1 year 7 months 6 days
Nonvested at the beginning of the period (in shares)					2,141,047
Granted (in shares)					956,312
Vested (in shares)					735,825
Nonvested at the end of the period (in shares)		2,203,810	2,141,047		2,203,810		2,141,047
Granted (in dollars per share)					$ 17.49
Performance Share Units
Equity Transactions
Stock based compensation expense		$ 3.0	$ 3.8	$ 0.0	$ 3.5	$ 0.0
Percentage of target award probable at the highest level							150.00%
Board of Directors certified that MPS schools were not in academic jeopardy	97.00%
Unrecognized compensation		$ 1.4			$ 1.4
Nonvested at the beginning of the period (in shares)					1,043,602
Granted (in shares)					138,241
Vested (in shares)					103,687
Nonvested at the end of the period (in shares)		1,008,156	1,043,602		1,008,156		1,043,602
Granted (in dollars per share)					$ 18.07
Performance Share Units \| Actual performance exceeds the target criteria
Equity Transactions
Stock based compensation expense					$ 5.6
Performance Shares Tranche #1
Equity Transactions
Granted (in shares)	446,221
Granted due to the Outperform level (in shares)	138,241
Performance Shares Tranche #2
Equity Transactions
Stock based compensation expense		$ 2.5			$ 0.0
Unrecognized compensation								$ 3.5
Mr. Davis \| Performance Shares Tranche #1
Equity Transactions
Granted (in shares)	90,000
Mr. Udell \| Performance Shares Tranche #1
Equity Transactions
Granted (in shares)	70,021