Stock Option Activity (Detail) - Stock Option [Member] - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options Outstanding, Beginning Balance	838,494
Stock Options Granted, Number of Shares	268,538	590,647	250,000
Stock Options Exercised, Number of Shares	0
Stock Options Canceled, Forfeited or Expired, Number of Shares	(98,875)
Number of Options Outstanding, Ending Balance	1,008,157	838,494
Stock Options Exerciseable, Number of Shares	281,458
Options Outstanding, Beginning Balance, Weighted Average Exercise Price	$ 30.18
Stock Options Granted, Weighted Average Exercise Price	37.21
Stock Options Exercised, Weighted Average Exercise Price	0
Stock Options Canceled, Forfeited or Expired, Weighted Average Exercise Price	35.45
Options Outstanding, Ending Balance, Weighted Average Exercise Price	$ 31.54	$ 30.18
Options Outstanding, Weighted Average Contractual Life	8 years 5 months 1 day	9 years 3 months 22 days
Stock Options Exerciseable, Weighted Average Exercise Price	$ 28.86
Stock Options Exerciseable, Weighted Average Contractual Life	8 years 2 months 16 days
Fair Value	$ 25.99
Forward Interest Rate, Minimum	1.19%
Forward Interest Rate, Maximum	1.58%
Expected Volatility Rate, Maximum	54.89%
Expected Volatility Rate, Minimum	53.44%
Unrecognized compensation expense related to non-vested stock awards	$ 7.2
Non-vested stock award compensation expense weighted-average period, years	2 years 1 month 6 days
Stock Compensation Expense	$ 6.3	$ 3.8	$ 0.1
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected Term	6 years 3 months
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected Term	5 years 10 months 10 days

The calculated fair value of a stock-based compensation award

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Unrecognized cost of unvested share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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.

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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.

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

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

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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.

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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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- Definition

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

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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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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.

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

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