Significant Accounting Policies (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 02, 2018
Significant Accounting Policies [Line Items]
Goodwill impairment loss	$ 0
Impairment of intangible assets	0
Impairment of cost method investment	0	$ 0	$ 0
Interest paid	0	0	0
Income tax payments	0	0	0
Fixed assets purchased	0	$ 0	$ 0
GovDelivery
Significant Accounting Policies [Line Items]
Escrow deposit	6,700,000
Employee Severance
Significant Accounting Policies [Line Items]
Severance costs	11,000,000
Accrued severance	8,500,000
Severance paid	$ 2,500,000
Subsequent Event | FolioDynamix
Significant Accounting Policies [Line Items]
Escrow deposit				$ 1,500,000