Incentive Plan - Summary of Stock Options Outstanding (Detail) (USD $)	12 Months Ended
Dec. 31, 2014
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Options Outstanding	1,751,270
Weighted Average Remaining Contractual Life, Options Outstanding	5 years 8 months 12 days
Weighted Average Exercise Price, Options Outstanding	$ 15.94
Number Of Options Exercisable	1,003,075
Weighted Average Remaining Contractual Life, Options Exercisable	4 years
Weighted Average Exercise Price, Options Exercisable	$ 16.42
Exercise Prices From 10.00 to 12.28 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices Lower Limit	$ 10.00
Exercise Prices Higher Limit	$ 12.28
Number of Options Outstanding	296,541
Weighted Average Remaining Contractual Life, Options Outstanding	4 years 10 months 24 days
Weighted Average Exercise Price, Options Outstanding	$ 10.60
Number Of Options Exercisable	250,621
Weighted Average Remaining Contractual Life, Options Exercisable	4 years 10 months 24 days
Weighted Average Exercise Price, Options Exercisable	$ 10.70
Exercise Prices From 13.83 to 14.62 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices Lower Limit	$ 13.83
Exercise Prices Higher Limit	$ 14.62
Number of Options Outstanding	672,750
Weighted Average Remaining Contractual Life, Options Outstanding	7 years 2 months 12 days
Weighted Average Exercise Price, Options Outstanding	$ 14.13
Number Of Options Exercisable	258,850
Weighted Average Remaining Contractual Life, Options Exercisable	6 years 10 months 24 days
Weighted Average Exercise Price, Options Exercisable	$ 14.00
Exercise Prices From 16.06 to 17.75 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices Lower Limit	$ 16.06
Exercise Prices Higher Limit	$ 17.75
Number of Options Outstanding	454,855
Weighted Average Remaining Contractual Life, Options Outstanding	7 years
Weighted Average Exercise Price, Options Outstanding	$ 17.37
Number Of Options Exercisable	166,480
Weighted Average Remaining Contractual Life, Options Exercisable	3 years 2 months 12 days
Weighted Average Exercise Price, Options Exercisable	$ 16.81
Exercise Prices From 20.25 to 22.17 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices Lower Limit	$ 20.25
Exercise Prices Higher Limit	$ 22.17
Number of Options Outstanding	150,570
Weighted Average Remaining Contractual Life, Options Outstanding	2 years 1 month 6 days
Weighted Average Exercise Price, Options Outstanding	$ 21.51
Number Of Options Exercisable	150,570
Weighted Average Remaining Contractual Life, Options Exercisable	2 years 1 month 6 days
Weighted Average Exercise Price, Options Exercisable	$ 21.51
Exercise Prices From 22.24 to 23.47 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices Lower Limit	$ 22.24
Exercise Prices Higher Limit	$ 23.47
Number of Options Outstanding	176,554
Weighted Average Remaining Contractual Life, Options Outstanding	1 year 1 month 6 days
Weighted Average Exercise Price, Options Outstanding	$ 23.42
Number Of Options Exercisable	176,554
Weighted Average Remaining Contractual Life, Options Exercisable	1 year 1 month 6 days
Weighted Average Exercise Price, Options Exercisable	$ 23.42

The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(iii)

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

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- Definition

Weighted average remaining contractual term of exercisable stock options, 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

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The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

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

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The number of shares reserved for issuance pertaining to the outstanding exercisable stock options as of the balance sheet date in the customized range of exercise prices for which the market and performance vesting condition has been satisfied.

+ 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 (c)(iii)

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

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The number of shares reserved for issuance pertaining to the outstanding stock options as of the balance sheet date for all option plans in the customized range of exercise prices.

+ 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 (c)(1)(i)-(ii)

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

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The weighted average price as of the balance sheet date at which grantees could acquire the underlying shares with respect to all outstanding stock options which are in the customized range of exercise prices.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

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-Subparagraph (c)(1)(i)-(ii)

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

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Weighted average remaining contractual term of outstanding stock options, 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

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The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

+ 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 (g)

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