Concentration of Business, Significant Customers and Credit Risk Cash Equivalents (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Risks and Uncertainties [Abstract]
Money market fund accounts	$ 195,575	$ 127,900
Cash	50,381	97,243
Cash and cash equivalents	$ 245,956	$ 225,143	$ 245,088	$ 237,125	$ 110,247