Share-Based Compensation - Fair value measurement assumptions (Details) (2012 Plan, Restricted Stock Units (RSUs), Time-Based Vesting)	3 Months Ended	12 Months Ended
Mar. 31, 2015	Dec. 31, 2014
2012 Plan \| Restricted Stock Units (RSUs) \| Time-Based Vesting
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Volatility of A&B common stock	29.50%	25.40%
Average volatility of peer companies	34.20%	27.30%
Risk-free interest rate	0.70%	0.40%

Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Average Volatility Rate of Peers

No definition available.

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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

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)(ii)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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- Definition

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

+ 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)(iv)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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