Significant Accounting Policies Other Comprehensive Income (Loss) - Reclassifications out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Accounting Policies [Abstract]
Actuarial loss	$ 3,911	$ 3,629	$ 3,092
Amortization of prior service cost (credit)	(670)	840	(2,213)
Deferred income tax benefit	480	150	(168)
Amounts reclassified from accumulated other comprehensive income (loss) to net income (loss)	$ 3,721	$ 4,619	$ 711