Certain Financial Statement Information - Net loss per share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended													12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Schedule of Reconciliation of Shares Used to Calculate Basic and Diluted Net (Loss) Income Per Share
Net loss	$ 23,116	$ (7,284)	[1]	$ (32,383)	[2]	$ 10,857	[3]	$ (17,606)	[4],[5]	$ (71,562)	[6]	$ (21,557)	$ (23,390)	$ (5,694)	$ (134,115)	$ (82,688)
Shares used in net loss per share computation:
Weighted average common shares outstanding, basic (shares)	75,629	73,989	[1]	72,610	[2]	69,360	[3]	67,566	[4],[5]	66,113	[6]	64,947	62,409	72,897	65,258	62,245
Net effect of dilutive common share equivalents (shares)														0	0	0
Weighted average common shares outstanding, diluted (shares)	77,193	73,989	[1]	72,610	[2]	70,234	[3]	67,566	[4],[5]	66,113	[6]	64,947	62,409	72,897	65,258	62,245
Basic and diluted net loss per share (USD per share)														$ (0.08)	$ (2.06)	$ (1.33)

[1] The consolidated operating results for the third quarter of fiscal 2014 included a charge of $2.9 million related to the Veloce consideration.

[2] The consolidated operating results for the second quarter of fiscal 2014 included a charge of $30.4 million related to the Veloce consideration.

[3] The consolidated operating results for the first quarter of fiscal 2014 included a charge of $9.3 million related to the Veloce consideration and a gain on sale of TPack of $19.7 million.

[4] The consolidated operating results for the fourth quarter of fiscal 2013 included a charge of $9.6 million related to the Veloce consideration.

[5] During fiscal 2012, one significant product development milestone relating to the Veloce project was considered probable of achievement and accordingly $60.4 million was recognized as research and development expense (see further discussion in Note 4, Veloce, to the Consolidated Financial Statements). However, approximately $8.0 million of the R&D expense was incorrectly recognized as this expense amount related to Unallocated Veloce Units that had not yet been distributed as of March 31, 2012. R&D expenses were also recognized during the first three quarters of fiscal 2013 in connection with further progress made in connection with the performance milestones relating to Veloce. However, the R&D expenses recognized during the first three quarters of fiscal 2013 also incorrectly included immaterial amounts related to the Unallocated Veloce Units. During the fourth quarter of fiscal 2013, the Company corrected the error impacting fiscal 2012 and the first three quarters of fiscal 2013. The correction of the errors resulted in a reduction of R&D expenses recognized by $10.4 million during the fourth quarter of fiscal 2013.

[6] During the fiscal years ended March 31, 2014, 2013 and 2012, the Company recognized an impairment charge of its non-marketable strategic investment of $0.0 million, $2.3 million and $1.0 million, respectively. Refer to Note 1, Summary of Significant Accounting Policies, to the Consolidated Financial Statements for details.