LEASES - Components of Lease Expense (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Leases
Expense associated with operating leases			$ 6,900	$ 6,800	$ 6,400
Operating Lease Cost	$ 1,445	$ 2,927
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows from operating leases	1,402	2,797
Right-of-use assets obtained in exchange for new operating lease liabilities	231	951
Reduction to right-of-use asset resulting from reduction to lease liability	1,279	1,279
Operating lease right-of-use assets	$ 24,449	$ 24,449
Operating lease, right-of-use asset, Statement of Financial Position	us-gaap:OtherAssets	us-gaap:OtherAssets
Operating lease liabilities	$ 26,640	$ 26,640
Operating lease liability, Statement of Financial Position	us-gaap:OtherLiabilities	us-gaap:OtherLiabilities
Weighted-average remaining lease term - operating leases	5 years 1 month 17 days	5 years 1 month 17 days
Weighted-average discount rate - operating leases	2.33%	2.33%
Minimum
Leases
Remaining lease terms - operating leases		1 year
Maximum
Leases
Remaining lease terms - operating leases		16 years