NATURE OF OPERATIONS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Other Assets (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) investment	Dec. 31, 2016 USD ($)
Other Assets
Total other assets	$ 241,645	$ 220,630
Unfunded commitments related to private equity investment funds	10,700	13,500
Impairment on investments	$ 3,300	2,500
Number of real estate investments impaired | investment	3
Other Assets
Other Assets
Equity and cost method investments	$ 184,255	168,572
Unamortized costs related to debt issuances	3,399	4,936
Deferred compensation plan assets	20,494	9,906
Other	33,497	37,216
Total other assets	$ 241,645	$ 220,630