Concentration of Business, Significant Customers and Credit Risk Cash Equivalents (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014
Risks and Uncertainties [Abstract]
Money market fund accounts	$ 198,992	$ 195,575
Cash	92,772	50,381
Cash and cash equivalents	$ 291,764	$ 245,956	$ 225,143	$ 245,088