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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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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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General descriptive information regarding an arrangement under which employees and directors receive: (a) awards of equity shares, equity share options, or other equity instruments; or (b) the entity incurs liabilities to them: (1) in amounts based, at least in part, on the price of the entity's shares or other equity instruments; or (2) that require or may require settlement by issuance of the entity's shares. Such an arrangement is usually provided to employees and directors to compensate them, provide performance incentives to them, and to attract or retain their services. May also include pertinent information particular to a plan that is not elsewhere specified in the taxonomy.

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The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan.

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Number of additional shares authorized for issuance under an established share-based compensation plan.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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

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Maximum number of shares that may be issued in accordance with the plan as a proportion of outstanding capital stock.

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Amount of capitalized and expensed compensation cost from equity-based compensation arrangements.

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Period from grant date that an equity-based award expires, 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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Purchase price of common stock expressed as a percentage of its fair value.

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Stock Based Awards - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Feb. 28, 2009	Dec. 31, 2018	Dec. 31, 2017	Oct. 12, 2018	Mar. 31, 2014	Mar. 20, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved		2,835,101	1,026,674
Intrinsic value of stock option exercised		$ 0	$ 11,500,000
Stock options granted			227,450
Additional shares issued		269,535	261,329
Common stock, voting rights		One
Recognized compensation expense		$ 16,139,000	$ 13,349,000
Restricted stock unit remaining weighted average period		6 years 6 months
Employee Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period			4 years
Stock options, weighted-average grant date fair value			$ 11.10
Tax benefits realized from options and other share-based payment arrangements			$ 0
Weighted-average remaining vesting period		1 year 4 months 24 days
Unrecognized employee stock-based compensation		$ 2,200,000
Employee Stock Option [Member] \| Employee [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted		0
Restricted stock units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Recognized compensation expense		$ 3,200,000	$ 3,500,000
Approximate compensation expenses		$ 2,600,000
Restricted stock unit remaining weighted average period		2 years
2009 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period	4 years
Options vested , description		options granted generally vest over four years and vest at a rate of 25% upon the first anniversary of the issuance date and 1/36th per month thereafter
2014 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period		4 years
Options expiration period		10 years
Options vested , description		Options granted under the 2014 Plan have a contractual life of ten years and generally vest over four years and vest at a rate of 25% upon the first anniversary of the issuance date and 1/36th per month thereafter.
Number of shares reserved					700,000
Percentage of common stock issued and outstanding increase annually		4.50%
End date of automatic annual increase of shares reserved for issuance		Jan. 01, 2024
2014 Plan [Member] \| Incentive Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved		2,000,000
2010 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period		3 years
Options expiration period		10 years
Options vested , description		Options granted to employees and consultants under the Plan generally vest 25% after one year of service, and ratably on a monthly basis over the following three years. Options expire ten years from the date of grant.
Number of shares reserved				600,000
Employee service term for options granted		1 year
2017 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vesting period		3 years
Options expiration period		10 years
Options vested , description		Options granted to employees and consultants under the Plan generally vest 25% after one year of service, and ratably on a monthly basis over the following three years. Options expire ten years from the date of grant
Number of shares reserved				461,000
Employee service term for options granted		1 year
Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved						25,000
Percentage of common stock issued and outstanding increase annually		1.00%
End date of automatic annual increase of shares reserved for issuance		Jan. 01, 2024
Additional shares issued		50,000
Common stock, voting rights		Immediately after the grant would own stock possessing 5% or more of the total combined voting power or value of our common stock.
Percentage of stock possessing		5.00%
Rights to purchase stock that remains outstanding		$ 25,000
Offerings of purchase periods		27 months
Maximum employee subscription rate		15.00%
Maximum [Member] \| 2009 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options expiration period	10 years
Minimum [Member] \| 2009 Plan [Member] \| Incentive Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Price of options granted, percentage		100.00%
Minimum [Member] \| 2009 Plan [Member] \| 10% Shareholders [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Price of options granted, percentage		110.00%
Minimum [Member] \| 2014 Plan [Member] \| Incentive Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Price of options granted, percentage		100.00%
Minimum [Member] \| Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Price of options granted, percentage		85.00%