Related Party Transactions - Rental agreement (Details) - Office Rental	12 Months Ended
Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($) item	Dec. 31, 2015 USD ($) item
Other Agreements
Rent expense	$ 100,000	$ 100,000	$ 58,000
LLC owned by two officers
Other Agreements
Number of officers \| item		2	2	2
Rent expense	$ 0		$ 21,000	$ 23,000

Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Name:	us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration