Common Stock (Tables)

6 Months Ended

Jun. 30, 2018

Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan

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:



	Three Months Ended June 30,						Six Months Ended June 30,
	2018			2017			2018			2017
	(in thousands)

Stock-based compensation expense	$	5,518		$	5,372		$	10,779		$	9,826
Income tax benefit	(1,323		)	(2,010		)	(2,584		)	(3,676		)
Net stock-based compensation expense	$	4,195		$	3,362		$	8,195		$	6,150

Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity

The following table presents the changes in non-vested time-based RSUs to all employees, including executive officers, for the six months ended June 30, 2018:



	Shares		Weighted-Average Grant Date Fair Value per Share

Non-vested at December 31, 2017	472,132		$	60.23
Granted	373,788		49.73
Vested	(208,060	)	58.49
Forfeited	(26,878	)	58.12
Non-vested at June 30, 2018	610,982		54.49

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



	Six Months Ended June 30,
	2018		2017
	(in thousands, except per share data)

Total intrinsic value of time-based awards vested	$	10,482	$	13,103
Total intrinsic value of time-based awards non-vested	36,934		22,454
Market price per share as of June 30,	60.45		43.11
Weighted-average grant date fair value per share	49.73		67.02

Restricted Stock Awards, Market-Based, Valuation assumptions

he Compensation Committee awarded a total of 90,778 market-based PSUs to our executive officers during the six months ended June 30, 2018. In addition to continuous employment, the vesting of these shares is contingent on our total stockholder return ("TSR"), which is essentially our stock price change including any dividends as compared to the TSR of a group of peer companies. The shares are measured over a three-year period ending on December 31, 2020, and can result in a payout between 0 percent and 200 percent of the target PSUs awarded. The weighted-average grant date fair value per PSU granted was computed using the Monte Carlo pricing model using the following assumptions:



	Six Months Ended June 30,
	2018			2017

Expected term of award (in years)	3			3
Risk-free interest rate	2.4		%	1.4		%
Expected volatility	42.3		%	51.4		%
Weighted-average grant date fair value per share	$	69.98		$	94.02

Schedule of Nonvested Performance-based Units Activity

The following table presents the change in non-vested market-based awards during the six months ended June 30, 2018:



	Shares		Weighted-Average Grant Date Fair Value per Share

Non-vested at December 31, 2017	52,349		$	84.06
Granted	90,778		69.98
Forfeited	(4,128	)	94.02
Non-vested at June 30, 2018	138,999		74.57

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



	Six Months Ended June 30,
	2018		2017
	(in thousands, except per share data)

Total intrinsic value of market-based awards non-vested	$	8,402	$	3,297
Market price per common share as of June 30,	60.45		43.11
Weighted-average grant date fair value per share	69.98		94.02