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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Represents the compensation cost capitalized during the period arising from equity-based compensation arrangements (for example, shares of stock, units, 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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Unrecognized cost of unvested share-based awards, other than options, awarded to employees as compensation.

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Unrecognized cost of unvested options awarded to employees as compensation.

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Amount of cash inflow from realized tax benefit related to deductible compensation cost reported on the entity's tax return for equity instruments in excess of the compensation cost for those instruments recognized for financial reporting purposes.

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Amount of cash outflow for realized tax benefit related to deductible compensation cost reported on the entity's tax return for equity instruments in excess of the compensation cost for those instruments recognized for financial reporting purposes.

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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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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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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Stock-Based Compensation - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation	$ 5,400,000	$ 3,100,000	$ 17,755,000	$ 9,378,000
Excess tax benefit related to stock-based compensation, decrease in operating activities			(22,114,000)	(21,987,000)
Excess tax benefits related to stock-based compensation			22,114,000	$ 21,987,000
Total unrecognized stock-based compensation expense	52,900,000		$ 52,900,000
Unrecognized compensation expense recognition period			3 years 1 month 6 days
Options, Granted			131,816	1,496,861
Aggregate intrinsic value of awards exercised	13,800,000	4,600,000	$ 26,900,000	$ 82,600,000
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation	2,500,000	2,300,000	$ 9,500,000	7,800,000
Unrecognized compensation expense recognition period			2 years 7 months 6 days
Unrecognized stock-based compensation expense	19,500,000		$ 19,500,000
Restricted Stock Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation	0	600,000	1,700,000	1,300,000
Fair value of awards vested during the period			1,700,000
Unrecognized compensation expense related to share based awards other than options	$ 0		$ 0
Non-vested restricted stock units or awards	0		0		67,744
Weighted average grant date fair value	$ 0		$ 0		$ 42.01
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation	$ 2,900,000	200,000	$ 6,600,000	300,000
Unrecognized compensation expense recognition period			3 years 3 months 18 days
Fair value of awards vested during the period	700,000		$ 1,500,000
Unrecognized compensation expense related to share based awards other than options	$ 33,400,000		$ 33,400,000
Non-vested restricted stock units or awards	1,609,607		1,609,607		888,483
Weighted average grant date fair value	$ 27.91		$ 27.91		$ 27.85
Website and software development cost
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation capitalized as website and software development cost	$ 600,000	$ 100,000	$ 1,400,000	$ 300,000