Subsequent Events - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	9 Months Ended
	Jan. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Subsequent Event [Line Items]
Common stock, shares issued		109,322,626	104,551,466
At-The-Market Facility [Member]
Subsequent Event [Line Items]
Common stock, shares issued		3,793,758
Net proceeds from sale of common stock		$ 7.1
Subsequent Event [Member] | At-The-Market Facility [Member]
Subsequent Event [Line Items]
Common stock, shares issued	1,500,000
Subsequent Event [Member] | At-The-Market Facility [Member] | Minimum [Member]
Subsequent Event [Line Items]
Net proceeds from sale of common stock	$ 2.1