Summary of Significant Accounting Policies - Additional Information (Detail)			12 Months Ended
	Jun. 30, 2016 USD ($)	May 26, 2016 USD ($) $ / shares	Dec. 31, 2016 USD ($) Segment $ / shares shares	Dec. 31, 2015 USD ($) $ / shares	Dec. 31, 2014 USD ($)
Summary Of Significant Accounting Policy [Line Items]
Excess tax benefits related to share based payments in provision for income taxes			$ 7,000,000	$ 0
Number of operating segments | Segment			1
Interest costs incurred			$ 1,300,000	1,300,000	$ 3,700,000
Interest costs capitalized			$ 400,000		400,000
Capitalized and amortized period			3 years 7 months 6 days
Total capitalized payroll costs related to internal use software projects			$ 8,800,000	4,300,000
Amortization expense related to capitalized software costs			3,600,000	1,800,000	900,000
Goodwill impairment amount	$ 0		0	0	0
Impairment of intangible assets with finite lives			0	0	0
Impairment of long-lived assets			$ 0	$ 0	0
Common stock, par value | $ / shares			$ 0.01	$ 0.01
Conversion fees, deferred revenue recognition period			10 years
Advertising costs			$ 4,900,000	$ 3,600,000	4,200,000
Sales taxes			$ 4,300,000	3,700,000	$ 3,000,000
Expected life of client relationships			10 years
Stock Repurchase Plan [Member]
Summary Of Significant Accounting Policy [Line Items]
Common stock, par value | $ / shares		$ 0.01
Stock repurchase plan period		24 months
Number of common stocks repurchased during the period | shares			1,122,261
Stock repurchased, average costs per share | $ / shares			$ 44.52
Stock Repurchase Plan [Member] | Restricted Stock [Member]
Summary Of Significant Accounting Policy [Line Items]
Shares withheld to satisfy tax withholding obligations | shares			302,424
Internal use Software [Member]
Summary Of Significant Accounting Policy [Line Items]
Capitalized and amortized period			3 years
Maximum [Member]
Summary Of Significant Accounting Policy [Line Items]
Interest costs capitalized				100,000
Maximum [Member] | Stock Repurchase Plan [Member]
Summary Of Significant Accounting Policy [Line Items]
Stock repurchase plan, authorization amount		$ 50,000,000
Net Long-Term Debt, Less Current Portion [Member]
Summary Of Significant Accounting Policy [Line Items]
Change in adoption of recent accounting pronouncements on other assets and long term debt				(100,000)
Deposits and Other Assets [Member]
Summary Of Significant Accounting Policy [Line Items]
Change in adoption of recent accounting pronouncements on other assets and long term debt				$ (100,000)