Income tax (benefit) provision from continuing operations (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Results of Operations, Income before Income Taxes [Abstract]
U.S.	$ (279,304)	$ (75,515)	$ (944)
Foreign	369,091	356,808	346,851
Income before income taxes	89,787	281,293	345,907
Current Income Tax Expense (Benefit), Continuing Operations [Abstract]
Current Federal Tax Expense (Benefit)	21,287	(3,966)	(3,185)
Current State and Local Tax Expense (Benefit)	1,004	(188)	(24)
Current Foreign Tax Expense (Benefit)	23,792	21,947	16,602
Current Income Tax Expense (Benefit)	46,083	17,793	13,393
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Deferred Federal Income Tax Expense (Benefit)	(114,743)	(42,207)	(22,641)
Deferred State and Local Income Tax Expense (Benefit)	(5,409)	(1,990)	(1,562)
Deferred Foreign Income Tax Expense (Benefit)	(6,736)	(16,228)	(8,608)
Deferred Income Tax Expense (Benefit)	(126,888)	(60,425)	(32,811)
Income tax benefit	(80,805)	(42,632)	(19,418)
Excess tax benefit from share-based compensation	2,400	800	1,200
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Computed expected income tax provision	31,425	98,453	121,067
State income taxes, net of federal benefits	(4,609)	(1,246)	(20)
Research and development tax credits - current year	(12,852)	(13,542)	(9,703)
Research and development tax credits - prior years	0	(2,511)	(1,789)
Foreign income taxed at lower than the federal rate	(105,069)	(114,497)	(106,939)
Increases related to current and prior year tax positions	53,695	14,462	19,769
Decreases related to prior year tax positions (1)	(36,297)	(12,103)	(33,100)
Withholding taxes	5,643	5,970	5,218
Change in valuation allowance	1,814	(2,482)	(14,286)
Intercompany prepaid tax asset amortization	7,931	(15,493)	(1,089)
Share-based compensation	(24,998)	0	0
Other	2,512	357	1,454
Income tax benefit	$ (80,805)	$ (42,632)	$ (19,418)
Increase of basic net income per share due to release of prior year tax positions	$ 0.17	$ 0.06	$ 0.16
Increase of diluted net income per share due to release of prior year tax positions	$ 0.15	$ 0.06	$ 0.15
Income tax holiday, aggregate dollar amount	$ 25,300	$ 6,000	$ 12,400
Undistributed earnings of foreign subsidiaries	4,300,000
Tax adjustments, settlements, and unusual provisions	$ 36,300
Other adjustments, percent		40.40%