Stock-based Compensation and Outstanding Awards (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Significant Assumptions Used to Calculate the Grant Date Fair Market Values of Options Granted

For the stock options granted in 2017, 2016 and 2015, the fair value of each option award was estimated on the date of grant using the Black-Scholes framework that uses the assumptions noted in the table below.

	December 31,
	2017			2016			2015
Valuation Assumptions:
Expected volatility		37.9	%		44.0	%		41.2	%
Risk-free interest rate		1.9	%		1.3	%		1.4	%
Expected dividends (per share)	$	—		$	—		$	—
Expected term (in years)		4.5			4.5			4.5

Summary of Stock Option Activity

The following table summarizes award activity for stock options:

Stock Options	Shares (in thousands)			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term		Aggregate Intrinsic Value (in millions)
Outstanding as of December 31, 2016		4,853		$	26.83
Granted		915			20.64
Forfeited		(102	)		23.23
Exercised		(36	)		14.19
Outstanding as of December 31, 2017		5,630		$	25.97		4.9	$	—
Exercisable at December 31, 2017		3,964		$	29.16		4.5	$	—

Summary of Status of Nonvested Shares of RSAs and RSUs

The following table summarizes award activity for restricted stock awards and restricted stock units:

RSAs / RSUs	Shares (in thousands)			Weighted- Average Grant-Date Fair Value
Nonvested as of December 31, 2016		2,311		$	27.66
Granted		580			15.87
Vested(1)		(808	)		22.34
Forfeited		(405	)		28.28
Nonvested as of December 31, 2017		1,678		$	25.99

⁽¹⁾ 251 thousand shares were withheld and retired from the vesting of shares to employees to satisfy minimum tax withholding.

The following table summarizes award activity for performance stock awards:

PSAs	Shares (in thousands)		Weighted- Average Grant-Date Fair Value
Nonvested as of December 31, 2016		233	$	18.81
Granted		84		22.75
Vested		—		—
Forfeited		—		—
Nonvested as of December 31, 2017		317	$	19.86