ACQUISITIONS - Acquisition of First Service Capital Management, Inc. (Details) $ in Thousands		9 Months Ended
	Feb. 17, 2017 USD ($) item	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Business Acquisition [Line Items]
Cash paid for acquisitions, net		$ (2,845)	$ 11,289
Goodwill		$ 136,303		$ 101,315
First Service Capital Management, Inc.
Business Acquisition [Line Items]
Cash paid for acquisitions, net	$ 1,400
Number of brokers of acquiree to be hired | item	4
Purchase price	$ 1,750
Goodwill	$ 660
Period for tax deduction purposes for goodwill and intangible assets	15 years
First Service Capital Management, Inc. | Customer relationship intangibles
Business Acquisition [Line Items]
Intangible asset recorded	$ 1,090
Intangible asset amortization period	15 years