STOCK-BASED COMPENSATION (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of Additional Information Concerning Restricted Stock Units

The following table summarizes additional information concerning restricted stock units at December 31, 2017:

	Restricted Stock Units		Weighted Average Grant Date Fair Value Per Unit
Unvested as of December 31, 2016	903,967		$	21.58
Granted	576,357		19.38
Vested	(333,338	)	25.30
Dividends reinvested	64,873		21.17
Cancelled/forfeited	(86,372	)	20.61
Unvested as of December 31, 2017	1,125,487		$	19.71

Summary of Assumptions Used in Total Stockholder Return-Based Stock Units Valuation

The following are the key assumptions used in this valuation:

	2017		2016		2015
Risk free interest rate	1.42% - 1.99%		0.78% - 1.60%		0.87% - 1.31%
Expected stock price volatility	28.86% - 30.97%		27.40% - 28.42%		23.55% - 27.02%
Expected service period	2.2 - 3.0 years		2.3 - 3.0 years		2.5 - 3.0 years
Expected dividend yield (assuming full reinvestment)	—	%	—	%	—	%