Amount of restricted investment in debt security measured at amortized cost (held-to-maturity).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 10
-Section S99
-Paragraph 3
-Subparagraph (SX 210.6-03(f))
-URI http://asc.fasb.org/extlink&oid=6488002&loc=d3e600178-122990

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

Marketable Securities and Held-to-Maturity Debt Securities - Held-to-Maturity Debt Securities (Details) - USD ($)	Jun. 30, 2020	Dec. 31, 2019
Held-to-Maturity Debt Securities
Held-to-maturity debt security	$ 0
Third lien senior secured notes subject to in-substance
Held-to-Maturity Debt Securities
Held-to-maturity debt security		$ 500,000,000