INDEBTEDNESS - Schedule of Line of Credit (Details) - Credit Agreement - Revolving Credit Facility - USD ($)	Mar. 31, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Capacity	$ 400,000,000.0	$ 400,000,000.0
Amount Borrowed	140,500,000	134,500,000
Letters of Credit Outstanding	5,200,000	5,200,000
Unused Capacity	$ 254,300,000	$ 260,300,000