Commitments and Contingencies - Additional Information (Detail) - Employee Severance [Member] $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2017 USD ($) Position Officer
Contingencies And Commitments [Line Items]
Separation charge	$ 5.1	$ 16.6
Stock-based compensation expense		4.5
Accounts Payable and Accrued Expenses [Member]
Contingencies And Commitments [Line Items]
Accrued separation charge	$ 5.5	5.5
Executive Management Transition [Member]
Contingencies And Commitments [Line Items]
Separation charge		9.4
Elimination [Member]
Contingencies And Commitments [Line Items]
Separation charge		$ 7.2
Total number of positions eliminated including officer level | Position		65
Number of positions eliminated | Officer		9