Intangible Assets - Intangible Assets, Other than Capitalized Software Development Costs (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Mar. 31, 2018
Finite Lived Intangible Assets [Line Items]
Gross carrying amount	$ 148,760	$ 148,760
Accumulated amortization	(85,533)	(74,669)
Net intangible assets	63,227	74,091
Customer Relationships
Finite Lived Intangible Assets [Line Items]
Gross carrying amount	54,450	54,450
Accumulated amortization	(37,819)	(35,531)
Net intangible assets	16,631	18,919
Computer Software, Intangible Asset
Finite Lived Intangible Assets [Line Items]
Gross carrying amount	94,310	94,310
Accumulated amortization	(47,714)	(39,138)
Net intangible assets	$ 46,596	$ 55,172