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Stock-Based Compensation Plans - Summary of Transactions of the Company's Stock Option Plans (Detail) - Stock Options Plan [Member]	9 Months Ended
	Sep. 30, 2015 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding, Number of Options, Beginning balance | shares	728,640
Exercised, Number of Options | shares	(132,614)
Forfeited, Number of Options | shares	(4,431)
Expired, Number of Options | shares	(20,552)
Outstanding, Number of Options, Ending balance | shares	663,810
Outstanding, Weighted Average Exercise Price, Beginning balance	$ 19.55
Exercised, Weighted Average Exercise Price	7.48
Forfeited, Weighted Average Exercise Price	14.63
Expired, Weighted Average Exercise	0.00
Outstanding, Weighted Average Exercise Price, Ending balance	$ 20.30
Discount [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Number of Options | shares	69,217
Granted, Weighted Average Exercise Price	$ 0.00
Granted, Weighted Average Grant-Date Fair Value	$ 37.55
Market Value [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Number of Options | shares	23,550
Granted, Weighted Average Exercise Price	$ 43.95
Granted, Weighted Average Grant-Date Fair Value	$ 9.89

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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Gross number of share options (or share units) granted during the period.

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Number of options outstanding, including both vested and non-vested options.

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