Stock-Based Compensation - Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
LTIPs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 2,551	$ 2,528	$ 2,619
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	0	42	163
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	5,106	2,150	1,992
Cost of sales | LTIPs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	654	729	720
Cost of sales | Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	0	21	81
Cost of sales | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	865	634	617
Selling, general and administrative expenses | LTIPs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,695	1,620	1,732
Selling, general and administrative expenses | Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	0	20	78
Selling, general and administrative expenses | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	4,195	1,490	1,352
Research and development | LTIPs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	202	179	167
Research and development | Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	0	1	4
Research and development | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 46	$ 26	$ 23