COMMON STOCK Common Stock (Tables)

12 Months Ended

Dec. 31, 2016

Equity [Abstract]

Schedule of Stock by Class [Table Text Block]

The following table provides a summary of our public offerings of common stock in 2016 and 2015:

Date	Shares Issued	Price per Share		Net Proceeds
				(in millions)
September 2016	9,085,000	$	61.51	$	558.5
March 2016	5,922,500	50.11		296.6
March 2015	4,002,000	50.73		202.9

Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block]

The following table provides a summary of the impact of our outstanding stock-based compensation plans on the results of operations for the periods presented:

	Year Ended December 31,
	2016			2015			2014
	(in thousands)
Stock-based compensation expense	$	19,502		$	20,068		$	17,518
Income tax benefit	(7,296		)	(7,636		)	(5,955		)
Net stock-based compensation expense	$	12,206		$	12,432		$	11,563

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

he Compensation Committee has awarded SARs to our executive officers in 2016, 2015, and 2014. The fair value of each SAR award was estimated on the date of grant using a Black-Scholes pricing model using the following assumptions:

	Year Ended December 31,
	2016			2015			2014
Expected term of award	6.0 years			5.2 years			6.0 years
Risk-free interest rate	1.8		%	1.4		%	2.1		%
Expected volatility	54.5		%	58.0		%	65.6		%
Weighted-average grant date fair value per share	$	26.96		$	22.23		$	29.96

Schedule of Share-based Compensation, Stock Appreciation Rights Award Activity [Table Text Block]

The following table presents the changes in our SARs for all periods presented:

	Year Ended December 31,
	2016							2015						2014
	Number of SARs		Weighted-Average Exercise Price		Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)		Number of SARs		Weighted-Average Exercise Price		Aggregate Intrinsic Value (in thousands)		Number of SARs	Weighted-Average Exercise Price		Aggregate Intrinsic Value (in thousands)
Outstanding beginning of year, January 1,	326,453		$	38.99	7.3	$	4,697	279,011		$	38.77	$	1,472	190,763	$	33.77	$	3,711
Awarded	58,709		51.63		—	—		68,274		39.63		—		88,248	49.57		—
Exercised	(141,084	)	40.16		—	2,770		(20,832	)	38.05		473		—	—		—
Outstanding at December 31,	244,078		41.36		6.9	7,620		326,453		38.99		4,697		279,011	38.77		1,472
Exercisable at December 31,	174,919		38.72		6.3	5,924		222,489		37.70		3,489		139,334	36.27		982

Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block]

The following table presents the changes in non-vested time-based awards during 2016:

	Shares		Weighted-Average Grant Date Fair Value
Non-vested at December 31, 2015	525,081		$	50.23
Granted	290,010		58.52
Vested	(317,034	)	48.61
Forfeited	(18,415	)	56.10
Non-vested at December 31, 2016	479,642		56.09

The following table presents the weighted-average grant date fair value per share and related information as of/for the periods presented:

	As of/Year Ended December 31,
	2016		2015		2014
	(in thousands, except per share data)
Total intrinsic value of time-based awards vested	$	18,973	$	17,077	$	18,278
Total intrinsic value of time-based awards non-vested	34,812		28,029		23,290
Market price per common share as of December 31,	72.58		53.38		41.27
Weighted-average grant date fair value per share	58.52		48.88		56.45

Restricted Stock Awards, Market-Based, Valuation assumptions [Table Text Block]

he weighted-average grant date fair value per market-based share for these awards granted was computed using the Monte Carlo pricing model using the following assumptions:

	Year Ended December 31,
	2016			2015
Expected term of award	3 years			3 years
Risk-free interest rate	1.2		%	0.9		%
Expected volatility	52.3		%	53.0		%
Weighted-average grant date fair value per share	$	72.54		$	66.16

Schedule of Nonvested Performance-based Units Activity [Table Text Block]

The following table presents the change in non-vested market-based awards during 2016:

	Shares		Weighted-Average Grant Date Fair Value per Share
Non-vested at December 31, 2015	71,549		$	63.60
Granted	24,280		72.54
Vested	(47,409	)	66.78
Non-vested at December 31, 2016	48,420		64.97

The following table presents the weighted-average grant date fair value per share and related information as of/for the periods presented:

	As of/Year Ended December 31,
	2016		2015		2014
	(in thousands, except per share data)
Total intrinsic value of market-based awards vested	$	6,562	$	4,293	$	1,260
Total intrinsic value of market-based awards non-vested	3,514		3,819		3,455
Market price per common share as of December 31,	72.58		53.38		41.27
Weighted-average grant date fair value per share	72.54		66.16		56.87