Benefit Plans - Summary of Company's Option Activity (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options, Beginning Balance	1,410,650	1,343,760	1,772,062
Number of Options, granted	881,800	456,200	203,600
Number of Options, exercised	(368,085)	(270,650)	(612,682)
Number of Options, cancelled/forfeited/expired	(339,930)	(118,660)	(19,220)
Number of Options, Ending Balance	1,584,435	1,410,650	1,343,760
Number of Options, Exercisable at December 31, 2016	354,165
Number of Options, Expected to Vest after December 31, 2016	1,107,243
Weighted-Average Price, Beginning Balance	$ 29.91	$ 27.25	$ 24.68
Weighted-Average Price, Options granted	25.26	31.69	32.79
Weighted-Average Price, Options exercised	27.34	19.81	21.55
Weighted-Average Price, Options cancelled/forfeited/expired	28.62	29.58	30.35
Weighted-Average Price, Ending Balance	28.14	$ 29.91	$ 27.25
Weighted-Average Price, Exercisable at December 31, 2016	30.85
Weighted-Average Price, Expected to Vest after December 31, 2016	$ 27.36
Weighted-Average Remaining Contractual Term, Balance At December 31, 2016	6 years 2 months 12 days
Weighted-Average Remaining Contractual Term, Exercisable at December 31, 2016	4 years 8 months 12 days
Weighted-Average Remaining Contractual Term, Expected to Vest after December 31, 2016	6 years 7 months 17 days
Aggregate Intrinsic Value, Balance At December 31, 2016	$ 17.5
Aggregate Intrinsic Value, Exercisable at December 31, 2016	3.0
Aggregate Intrinsic Value, Expected to Vest after December 31, 2016	$ 13.1

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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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.

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For presentations that combine terminations, 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 or that expired.

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Weighted average price of options that were either forfeited or expired.

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

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of fully vested and expected to vest options that are exercisable.

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As of the balance sheet date, the weighted-average exercise price (at which grantees can acquire the shares reserved for issuance) for exercisable stock options that are fully vested or expected to vest.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for fully vested and expected to vest options that are exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of share options (or share units) exercised during the current period.

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