Sale of Commercial Business - Summary of Charges Related to Restructuring Activities (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Restructuring Cost And Reserve [Line Items]
Accrued Restructuring Expenses at Dec 31, 2016		$ 774
Expenses	$ 809		$ 809
Accrued Restructuring Expenses at September 30, 2017		1,166
Commercial Business [Member]
Restructuring Cost And Reserve [Line Items]
Expenses		9,521
Less: Payments		8,434
Accrued Restructuring Expenses at September 30, 2017		1,087
Commercial Business [Member] | Severance Benefits and Related Costs [Member]
Restructuring Cost And Reserve [Line Items]
Expenses		9,521
Less: Payments		8,434
Accrued Restructuring Expenses at September 30, 2017		$ 1,087