Income Taxes - Income Tax Expense (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Dec. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Current
Federal		$ 80,339	$ 2,184	$ 11,971
State		3,437	1,576	2,443
Foreign		14,388	8,039	12,039
Total		98,164	11,799	26,453
Deferred
Federal		12,007	(20,287)	7,887
State		391	(3,446)	1,113
Foreign		(4,260)	(762)	(833)
Total		8,138	(24,495)	8,167
Income taxes
Income tax expense (benefit)		106,302	(12,696)	34,620
Actual income taxes differed from that obtained by applying the statutory federal income tax rate to income before income taxes
Computed expected income taxes		69,556	(2,445)	54,910
State income taxes, net of federal income tax benefit		9,044	(1,403)	1,298
Foreign rate differential		(37,090)	(8,062)	(28,233)
Unrecognized tax benefits		1,301	2,691	3,670
Income tax expense on diminution of operations and nondeductible goodwill		0	3,921	1,352
Foreign income withholding tax expense		262	432	0
Nontaxable income		(7,006)	(5,055)	0
US tax on deemed repatriated foreign earnings	$ 59,114	57,138	0	0
Re-measurement of deferred taxes		14,395	0	0
Statutory foreign income tax expense (benefit)		59	(2,504)	(477)
Other		(1,357)	(271)	2,100
Income tax expense (benefit)		$ 106,302	$ (12,696)	$ 34,620