Income Taxes - Federal income tax expense (benefit) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	12 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes
Current					$ (6)	$ 11
Deferred						1,134	$ (337)
Income tax expense (benefit)	$ 1,789	$ 3	$ 1,934	$ (4)	$ (6)	$ 1,145	$ (337)

Amount of deferred income tax expense (benefit) pertaining to income (loss) from continuing operations.

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