Stock-Based Compensation - Stock Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Summary of Stock-Based Compensation Expense of Stock Options and Restricted Stock Units
Stock-based compensation expense	$ 5,939	$ 4,228	$ 12,043	$ 9,426
Stock-based compensation (capitalized to) expensed from inventory	(5)	2	(17)	20
Total	5,934	4,230	12,026	9,446
Cost of Revenues
Summary of Stock-Based Compensation Expense of Stock Options and Restricted Stock Units
Stock-based compensation expense	121	100	226	129
Research and Development Expense
Summary of Stock-Based Compensation Expense of Stock Options and Restricted Stock Units
Stock-based compensation expense	3,955	2,776	8,015	6,047
Selling, General and Administrative
Summary of Stock-Based Compensation Expense of Stock Options and Restricted Stock Units
Stock-based compensation expense	1,863	1,352	3,802	3,250
Stock Options
Summary of Stock-Based Compensation Expense of Stock Options and Restricted Stock Units
Stock-based compensation expense	289	292	496	706
Restricted Stock Units (RSUs)
Summary of Stock-Based Compensation Expense of Stock Options and Restricted Stock Units
Stock-based compensation expense	$ 5,650	$ 3,936	$ 11,547	$ 8,720