Agreements with SK hynix and Micron (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended	22 Months Ended	16 Months Ended
	Mar. 31, 2015	Mar. 31, 2015	Mar. 31, 2015
SK hynix [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash Received to date in 2015	$ 12.0	$ 84.0
Estimated to Be Received in Remainder of 2015	36.0	36.0	36.0
Estimated to Be Received in 2016	48.0	48.0	48.0
Estimated to Be Received in 2017	48.0	48.0	48.0
Estimated to Be Received in 2018	24.0	24.0	24.0
Total Estimated Cash receipts	240.0	240.0	240.0
SK hynix [Member] | Royalty revenue
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash Received to date in 2015	11.8	82.7
Estimated to Be Received in Remainder of 2015	35.5	35.5	35.5
Estimated to Be Received in 2016	47.9	47.9	47.9
Estimated to Be Received in 2017	48.0	48.0	48.0
Estimated to Be Received in 2018	24.0	24.0	24.0
Total Estimated Cash receipts	238.1	238.1	238.1
SK hynix [Member] | Gain from settlement
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash Received to date in 2015	0.2	1.3
Estimated to Be Received in Remainder of 2015	0.5	0.5	0.5
Estimated to Be Received in 2016	0.1	0.1	0.1
Estimated to Be Received in 2017	0	0	0
Estimated to Be Received in 2018	0	0	0
Total Estimated Cash receipts	1.9	1.9	1.9
Micron [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash Received to date in 2015	10.0		55.5
Estimated to Be Received in Remainder of 2015	30.0	30.0	30.0
Estimated to Be Received in 2016	40.0	40.0	40.0
Estimated to Be Received in 2017	40.0	40.0	40.0
Estimated to Be Received in 2018	40.0	40.0	40.0
Estimated to Be Received in 2019	40.0	40.0	40.0
Estimated to Be Received in 2020	34.5	34.5	34.5
Total Estimated Cash receipts	280.0	280.0	280.0
Micron [Member] | Royalty revenue
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash Received to date in 2015	9.7		53.7
Estimated to Be Received in Remainder of 2015	29.0	29.0	29.0
Estimated to Be Received in 2016	39.5	39.5	39.5
Estimated to Be Received in 2017	40.0	40.0	40.0
Estimated to Be Received in 2018	40.0	40.0	40.0
Estimated to Be Received in 2019	40.0	40.0	40.0
Estimated to Be Received in 2020	34.5	34.5	34.5
Total Estimated Cash receipts	276.7	276.7	276.7
Micron [Member] | Gain from settlement
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cash Received to date in 2015	0.3		1.8
Estimated to Be Received in Remainder of 2015	1.0	1.0	1.0
Estimated to Be Received in 2016	0.5	0.5	0.5
Estimated to Be Received in 2017	0	0	0
Estimated to Be Received in 2018	0	0	0
Estimated to Be Received in 2019	0	0	0
Estimated to Be Received in 2020	0	0	0
Total Estimated Cash receipts	$ 3.3	$ 3.3	$ 3.3