BUSINESS ACQUISITIONS - Comfort Infusion, Inc. (Details) - USD ($) $ in Thousands		1 Months Ended	12 Months Ended
	Mar. 22, 2017	Jul. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	May 08, 2017	Dec. 31, 2016	Dec. 31, 2014
Summary of the preliminary fair value determination of the acquired assets and liabilities
Definite-lived intangible assets					$ 7,730
Goodwill			$ 832,624	$ 609,592		$ 316,616	$ 256,318
Comfort Infusion, Inc.
BUSINESS ACQUISITIONS
Cash	$ 10,613
Contingent consideration at fair value	3,800	$ 2,000
Total	14,413
Maximum additional cash payouts per performance period	2,000
Maximum payout of contingent consideration	6,000
Fair value of contingent liability			4,300	$ 3,760
Purchase consideration deposited into an escrow account	$ 1,050
Deposit term into an escrow account	18 months
Acquisition-related costs charged to Selling, general, and administrative expenses			$ 204
Summary of the preliminary fair value determination of the acquired assets and liabilities
Cash	$ 104
Accounts receivable	575
Inventories	118
Prepaid expenses and other current assets	15
Definite-lived intangible assets	2,400
Other noncurrent assets	5
Accounts payable	(372)
Accrued expenses - other	(101)
Total identifiable net assets	2,744
Goodwill	11,669
Total acquisition price	14,413
Physician relationships | Comfort Infusion, Inc.
Summary of the preliminary fair value determination of the acquired assets and liabilities
Definite-lived intangible assets	$ 1,200
Definite-lived intangible assets
Useful Life	7 years
Non-compete employment agreements | Comfort Infusion, Inc.
Summary of the preliminary fair value determination of the acquired assets and liabilities
Definite-lived intangible assets	$ 1,200
Definite-lived intangible assets
Useful Life	5 years