COMMITMENTS AND CONTINGENCIES - Leases (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Leases
2018	$ 7,739,000
2019	5,010,000
2020	3,688,000
2021	2,559,000
2022	1,829,000
2023 and Thereafter	4,891,000
Total Future Minimum Lease Payments	25,716,000
Capital Leases
2018	1,722,000
2019	754,000
2020	387,000
2021	0
2022	0
2023 and Thereafter	0
Total Future Minimum Lease Payments	2,863,000
Total
2018	9,461,000
2019	5,764,000
2020	4,075,000
2021	2,559,000
2022	1,829,000
2023 and Thereafter	4,891,000
Total Future Minimum Lease Payments	28,579,000
Rent expense for leased facilities and equipment	7,700,000	$ 7,300,000	$ 7,200,000
Purchase commitments outstanding	$ 0
Minimum
Future minimum lease payment for operating and capital leases
Capital lease interest rate	3.00%
Maximum
Future minimum lease payment for operating and capital leases
Capital lease interest rate	7.00%