Employee Benefit Plans - Employee incentive programs (Details) - USD ($)	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Profit Sharing Plan
Employee incentive programs
Employer contribution under plan (in dollars)	$ 0	$ 0	$ 0
401 (k) Plan
Employee incentive programs
Employer contribution under plan (in dollars)	$ 881,000	$ 716,000	$ 495,000
Employer matching contribution (as a percent)	50.00%
Vesting period of employer matching contributions	3 years