Prior Periods Financial Statement Revision - Schedule of Correction of Misstatements on Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Changes And Error Corrections [Line Items]
Share-based compensation expense	$ 5,496	$ 3,935	$ 4,039
As Previously Reported [Member]
Accounting Changes And Error Corrections [Line Items]
Share-based compensation expense		4,270	3,704
Adjustment [Member]
Accounting Changes And Error Corrections [Line Items]
Share-based compensation expense		$ (335)	$ 335