Common Stock (Tables)

3 Months Ended

Mar. 31, 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 March 31,
	2018			2017
	(in thousands)

Stock-based compensation expense	$	5,261		$	4,453
Income tax benefit	(1,261		)	(1,666		)
Net stock-based compensation expense	$	4,000		$	2,787

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

The following table presents the changes in non-vested time-based awards to all employees, including executive officers, for the three months ended March 31, 2018:



	Shares		Weighted-Average Grant Date Fair Value per Share

Non-vested at December 31, 2017	472,132		$	60.23
Granted	136,256		50.94
Vested	(66,253	)	58.16
Forfeited	(5,800	)	68.18
Non-vested at March 31, 2018	536,335		58.04

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



	As of/Three Months Ended March 31,
	2018		2017
	(in thousands, except per share data)

Total intrinsic value of time-based awards vested	$	3,530	$	3,602
Total intrinsic value of time-based awards non-vested	26,297		33,366
Market price per share as of March 31,	49.03		62.35
Weighted-average grant date fair value per share	50.94		73.28

Restricted Stock Awards, Market-Based, Valuation assumptions

he Compensation Committee of our Board of Directors awarded a total of 90,778 market-based restricted shares to our executive officers during the three months ended March 31, 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 total shares awarded. The weighted-average grant date fair value per market-based share for these awards was computed using the Monte Carlo pricing model using the following assumptions:



	Three Months Ended March 31,
	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 three months ended March 31, 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 March 31, 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:



	As of Three Months Ended March 31,
	2018		2017
	(in thousands, except per share data)

Total intrinsic value of market-based awards non-vested	$	6,815	$	4,769
Market price per common share as of March 31,	49.03		62.35
Weighted-average grant date fair value per share	69.98		94.02