Long-Term Debt - Schedule of Long Term Debt (Details) - USD ($)	Jun. 30, 2019	Dec. 31, 2018	Dec. 29, 2017
Debt Instrument [Line Items]
Long-term debt, net	$ 72,869,000	$ 72,500,000
Note Purchase Agreement | Senior Notes
Debt Instrument [Line Items]
Face amount	75,000,000	75,000,000	$ 75,000,000
Front end fees	(799,000)	(872,000)
Debt issuance costs	(1,742,000)	(1,902,000)
Back end fees	410,000	274,000
Long-term debt, net	$ 72,869,000	$ 72,500,000