SHAREHOLDERS' EQUITY - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands				1 Months Ended	12 Months Ended
	Jan. 03, 2018	Mar. 06, 2017	Jan. 18, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 25, 2018	Mar. 13, 2017
Subsidiary or Equity Method Investee [Line Items]
Issuance of common stock					$ 88,656	$ 0	$ 114,889
Payments for capital contribution				$ 110,000
Mr. Villari
Subsidiary or Equity Method Investee [Line Items]
Stock issued during period, shares, purchase of assets (in shares)			128,572
US Premium Financing Holding Company
Subsidiary or Equity Method Investee [Line Items]
Cost method investment ownership percentage			4.99%
US Premium Financing Holding Company
Subsidiary or Equity Method Investee [Line Items]
Price per share of the Company's common stock (in dollars per share)			$ 45.45
Cost method investments			$ 5,800
Underwritten Public Offering
Subsidiary or Equity Method Investee [Line Items]
Issuance of common stock (in shares)		2,012,500
Shares issued, price per share (in dollars per share)		$ 46.50
Issuance of common stock		$ 88,700
Public offering deduction amount		$ 4,900
Senior Subordinated Notes
Subsidiary or Equity Method Investee [Line Items]
Interest rate, stated percentage									5.75%
Subsequent Event | Mr. Villari
Subsidiary or Equity Method Investee [Line Items]
Stock issued during period, shares, purchase of assets (in shares)	114,285
Cash paid for purchase of shares of common stock	$ 12,500
Subsequent Event | US Premium Financing Holding Company
Subsidiary or Equity Method Investee [Line Items]
Cost method investment ownership percentage	25.01%							70.00%
Subsequent Event | US Premium Financing Holding Company
Subsidiary or Equity Method Investee [Line Items]
Cost method investments	$ 18,100