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Employee Benefit Plans - Stock options granted (Details) - Stock options - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Mar. 31, 2015
Weighted average assumptions used in estimating the grant date fair value of stock options granted      
Expected life - years 6 years 6 months 7 years 2 months 12 days 7 years 8 months 12 days
Risk-free interest rate (as a percent) 2.20% 1.90% 2.00%
Expected volatility of common stock (as a percent) 40.00% 47.00% 50.00%
Fair value and intrinsic value information      
Weighted average grant date fair value per share of options granted (in dollars per share) $ 2.11 $ 1.19 $ 1.01
Intrinsic value of options exercised (in dollars) $ 1,061 $ 135 $ 9