Share-Based Compensation - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Compensation expense	$ 0.1	$ 2.6	$ 2.9	$ 2.7
Unrecognized compensation expense		$ 4.2
Shares expected to be surrendered by employees		135,000
Surrender of common stock by employees		135,009
Fourth Amendment And Restated Equity Incentive Plan
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Authorized shares available for issuance		868,000