Concentration of Risks and Uncertainties (Details) $ in Thousands	Mar. 31, 2016 USD ($) issuer
Concentration Risk [Line Items]
Corporate debt securities	$ 193,389
U.S. Treasury Securities
Concentration Risk [Line Items]
U.S. Treasury securities	184,900
Corporate debt securities
Concentration Risk [Line Items]
Corporate debt securities	$ 8,400
Number of issuers \| issuer	1
Commercial paper
Concentration Risk [Line Items]
Number of issuers \| issuer	8
Commercial paper	$ 159,000

Unsecured short-term debt instrument issued by corporations which are highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Cash Equivalents
-URI http://asc.fasb.org/extlink&oid=6507016

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3052-108585

Name:	us-gaap_CommercialPaperAtCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant