Marketable Securities Marketable Securities (Details 1) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	$ 264,477	$ 226,708
Cash, fair value	41,389	51,056
Cash, Cash Equivalents and Short Term Investments, Fair Value Disclosure	305,866	277,764
Cash Equivalents [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	101,627	64,868
Short-term Investments [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	$ 162,850	$ 161,840

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty.

No definition available.

Name:	rmbs_CashFairValueDisclosure
Namespace Prefix:	rmbs_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant