Revenue - Additional Information (Detail)	6 Months Ended
	Sep. 30, 2018
Minimum [Member]
Supply Commitment [Line Items]
Long-term supply agreements maturity year	2018
Revenue from contract with customer collection terms	30 days
Maximum [Member]
Supply Commitment [Line Items]
Long-term supply agreements maturity year	2025
Revenue from contract with customer collection terms	65 days