Stock-Based Compensation - Assumptions Used to Compute Share-Based Compensation Costs for Stock Options Granted (Detail) - $ / shares	6 Months Ended						12 Months Ended
	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Weighted average grant date fair value of stock options							$ 1.40	$ 3.08
Assumptions
Risk-free interest rate (weighted average)	0.89%	0.47%	0.47%	0.18%	0.11%	0.40%	1.10%	1.10%
Weighted average expected life (years)	6 months	6 months	6 months	6 months	6 months	6 months	4 years 9 months 18 days	4 years
Volatility (weighted average)	64.20%	52.60%	40.40%	66.10%	103.80%	109.10%	74.30%	83.50%
Forfeiture rate							23.00%	23.30%