Net Loss Per Share - Additional Information (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity option
Earnings Per Share [Line Items]
Exercisable options outstanding that enable to purchase shares		750	825
Shares with dilutive effect and included in computation of diluted loss per share		127	319
Options excluded from computation of diluted loss per share due to anti-dilutive effect	120	220	260
Restricted stock
Earnings Per Share [Line Items]
Exercisable options outstanding that enable to purchase shares	755	169	141
Shares with dilutive effect and included in computation of diluted loss per share	103	17	26