SHARE-BASED PAYMENTS SHARE-BASED PAYMENTS (Tables)

12 Months Ended

Dec. 31, 2018

Restricted Stock Units Activity

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of Share-based Compensation, Activity

The following tables set forth activity and various statistics for our restricted stock unit awards:

	Number of Units		Weighted Average Price
Nonvested December 31, 2017	1,001,805		$	32.30
Granted	296,277		$	46.94
Released to participants	(243,289	)	$	39.26
Forfeited	(29,600	)	$	39.34
Nonvested December 31, 2018	1,025,193		$	34.68

	2018		2017		2016
Weighted-average grant date fair value (per share)	$	46.94	$	45.11	$	20.04
Fair value of units granted (thousands of dollars)	$	13,907	$	12,685	$	11,081
Fair value of units vested (thousands of dollars)	$	9,552	$	7,258	$	4,429

Performance-Unit Activity

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of Share-based Compensation, Activity

The following tables set forth activity and various statistics related to the performance unit awards and the assumptions used in the valuations at the respective grant dates:

	Number of Units		Weighted Average Price
Nonvested December 31, 2017	1,136,133		$	40.08
Granted	370,677		$	59.57
Released to participants	(257,807	)	$	48.66
Forfeited	(5,360	)	$	46.97
Nonvested December 31, 2018	1,243,643		$	44.08

	2018	2017	2016
Volatility (a)	39.20%	40.59%	39.94%
Dividend yield	5.49%	4.68%	11.32%
Risk-free interest rate	2.44%	1.49%	0.93%

(a) - Volatility was based on historical volatility over three years using daily stock price observations.

	2018		2017		2016
Weighted-average grant date fair value (per share)	$	59.57	$	56.65	$	25.54
Fair value of units granted (thousands of dollars)	$	22,081	$	17,621	$	15,229
Fair value of units vested (thousands of dollars)	$	12,545	$	8,704	$	—