Share-Based Compensation - Fair Value Assumptions of Stock Options (Details) - BYB Plan - $ / shares	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Time Options Grants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum		1.34%	1.68%
Risk-free interest rate, maximum		1.40%	1.85%
Expected stock price volatility		20.39%
Expected stock price volatility, minimum			16.18%
Expected stock price volatility, maximum			16.55%
Expected dividend yield		0.00%	0.00%
Weighted average grant date fair value		$ 3.55	$ 2.25
Time Options Grants \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)		5 years 2 months 12 days	5 years 8 months 12 days
Time Options Grants \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)		5 years 7 months 6 days	6 years 3 months 19 days
Performance Options Grants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	FY 2016 and FY 2015; Implied forward rates
Expected term (years)	FY 2016 and FY 2015; Variable
Expected stock price volatility, minimum		20.34%	16.18%
Expected stock price volatility, maximum		20.39%	16.55%
Expected dividend yield		0.00%	0.00%
Weighted average grant date fair value		$ 3.75	$ 1.65

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- Definition

Share based compensation arrangement by share based payment award fair value assumptions risk free interest rate description.

+ References

No definition available.

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- Definition

Agreed-upon price for the exchange of the underlying asset relating to the share-based payment award.

+ References

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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

+ References

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- Definition

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.

+ References

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- Definition

The estimated measure of the maximum 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.

+ References

No definition available.

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The estimated measure of the minimum 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.

+ References

No definition available.

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- Definition

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

+ References

No definition available.

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- Definition

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

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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.

+ References

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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.D.2)
-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

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