Stock-Based Compensation Plans (Tables)

12 Months Ended

Dec. 31, 2017

Stock-Based Compensation Plans [Abstract]

A summary of the Company’s stock-based award plan activity, including stock options and SARs, for the years ended December 31, 2017, 2016 and 2015 is presented in the following table (underlying shares in thousands).

Stock-Based Compensation Awards
	Shares			Weighted-Average Exercise Price (per share)		Wtd. Avg. Remaining Contractual Term (years)	Aggregate Intrisic Value of In-The-Money Options (in millions)
Outstanding at December 31, 2014		18,214		$	8.23
Granted		1,075		$	10.61
Settled		(304	)	$	8.33
Forfeited		(1,952	)	$	8.43
Outstanding at December 31, 2015		17,033		$	8.36
Granted		2,427		$	10.75
Settled		(1,980	)	$	8.18
Forfeited		(2,931	)	$	8.31
Converted to liability		(1,264	)	$	8.16
Outstanding at December 31, 2016		13,285		$	8.85
Granted		799		$	20.00
Settled		(193	)	$	8.17
Forfeited		(1,057	)	$	8.34
Outstanding at December 31, 2017		12,834		$	9.54	6.81	$ 313.1
Vested at December 31, 2017		9,459		$	9.05	6.59	$ 235.4

Assumptions Used to Estimate Fair Value of Options Granted

The following assumptions were used to estimate the fair value of options and SARs granted during the fiscal years ended December 31, 2017, 2016 and 2015.

	2017		2016		2015
Assumptions:
Expected life of options (in years)		5.00 - 6.25		5.10		4.80
Risk-free interest rate		1.9 - 2.1%		1.3%		1.6%
Assumed volatility		41.2 - 45.8%		49.5%		49.9%
Expected dividend rate		0.0%		0.0%		0.0%

Summary of Assumptions Used to Estimate Fair Value of DSUs Granted

The following assumptions were used to estimate the fair value of DSUs at the time of grant using the Finnerty discount for lack of marketability pricing model.

	2017
Assumptions:
Average length of holding period restrictions (years)		1.42
Assumed volatility		51.5	%