Employee Stock Purchase Plan - Summary of Employee Stock Purchase Plan (Detail) - USD ($)	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Employee Stock Purchase Plan [Line Items]
Employee contributions	$ 419,000	$ 371,000	$ 400,000
Shares acquired	2,460,867
Employee Stock Purchase Plan [Member]
Employee Stock Purchase Plan [Line Items]
Shares acquired	10,596	10,975	12,299
Average purchase price	$ 38.80	$ 33.81	$ 32.52