Investments - Unrealized Loss Position (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Investments
12 Months or Greater, Fair Value		$ 5,108
12 Months or Greater, Unrealized Losses		896
Unrestricted available-for-sale, Debt securities \| Corporate debt securities
Investments
12 Months or Greater, Fair Value	$ 2,832	1,843
12 Months or Greater, Unrealized Losses	$ 96	887
Restricted \| Short-term bond
Investments
12 Months or Greater, Fair Value		3,265
12 Months or Greater, Unrealized Losses		$ 9

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118955579&loc=SL82922890-210455

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27337-111563

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=118942371&loc=SL82922954-210456

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