Stock Options, Restricted Stock Units and Employee Stock Purchase Plan (Tables)

9 Months Ended

Sep. 30, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

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

The following table sets forth the components of the Company’s share-based compensation expense for the three and nine month periods ended September 30, 2018 and 2017 (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Stock options	$	2,357	$	3,190	$	7,993	$	9,461
Employee stock purchase plan	—		286		—		822
Restricted stock units	3,389		2,306		9,206		5,343
Total stock-based compensation expense	$	5,746	$	5,782	$	17,199	$	15,626

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions

Set forth in the following table are the weighted-average assumptions used in estimating the grant date fair value of the stock options granted under the Company's equity compensation plans during the nine month period ended September 30, 2017, along with the weighted-average grant date fair values:

	Three Months Ended September 30,						Nine Months Ended September 30,
	2018			2017			2018			2017
Expected volatility	—		%	—		%	—		%	50		%
Expected life (in years)	—			—			—			4.8
Risk-free interest rate	—		%	—		%	—		%	1.75		%
Dividend yield	—			—			—			—
Fair value per stock option	$	—		$	—		$	—		$	9.25
Forfeiture rate	—		%	—		%	—		%	8		%

Schedule of Share-based Compensation, Activity

The table below sets forth a summary of stock option activity within the Company’s stock-based compensation plans for the nine month period ended September 30, 2018: 

	Number of Options (in thousands)		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value (in thousands) (1)
Outstanding at December 31, 2017	4,053		$	28.95	4.56	$	21,459
Granted	—		—
Exercised	(22	)	24.99
Forfeited	(518	)	31.76
Outstanding at September 30, 2018	3,514		$	28.56	3.95	$	—
Exercisable at September 30, 2018	2,239		$	29.16	3.62	$	—

(1) The Aggregate Intrinsic Value of stock options outstanding and exercisable is defined as the difference between the market value of the Company’s common stock as of the date indicated and the exercise price of the stock options. Stock options for which the exercise price exceeded the market price have been omitted. Fluctuations in the intrinsic value of both outstanding and exercisable options may result from changes in underlying stock price and the timing and volume of option grants, exercises and forfeitures.

Schedule of Nonvested Restricted Stock Units Activity

Set forth below is a summary of unvested RSU activity during the nine month period ended September 30, 2018:

	Number of Units (in thousands)	Weighted Average Per Share Grant Date Fair Value
Unvested at December 31, 2017	888	$	32.56
Granted	1,320	$	19.27
Vested	(288)	$	32.91
Forfeited	(95)	$	24.59
Unvested at September 30, 2018	1,825	$	23.30