Common Stock Equity Incentive Plan (Tables)

3 Months Ended

Mar. 31, 2017

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

Authorized Increases of Common Stock under the 2009 Plan

The following table summarizes the authorized increases of common stock under the 2009 Plan:

Date Authorized	Authorized Shares Added
May 15, 2010	1,238,095
January 7, 2011	714,286
January 1, 2013	838,375
January 1, 2014	1,066,340
January 1, 2015	1,119,255
January 1, 2016	1,152,565
January 1, 2017	1,166,546

Stock Option Activity

The following table summarizes the stock option activity, including options with performance conditions, for the three months endedMarch 31, 2017:

	Number of options		Weighted average exercise price		Weighted average remaining contractual term (years)
Outstanding at beginning of period	6,278,542		$	14.93	5.8
Options granted	1,286,283		10.89
Options exercised	(8,741	)	7.29
Options forfeited	(11,470	)	27.44
Options expired	(10,919	)	43.19
Outstanding at end of period	7,533,695		$	14.19	6.3
Options exercisable at end of period	4,950,721		$	11.76	4.8

Assumptions Used in Black-Scholes Pricing Model for New Grants

The following table summarizes the range of assumptions used to estimate the fair value of stock options granted, including those options granted with a market condition, during the three months endedMarch 31, 2017:

Risk-free interest rate	2.0% to 2.2%
Expected dividend yield	—%
Expected volatility	68.9% to 69.2%
Expected term (in years)	6.9 to 7.8
Weighted-average grant-date fair value per share	$7.24

Restricted Stock Activity

A summary of the Company's unvested restricted stock, including restricted stock with performance conditions, at March 31, 2017 and changes during the three months endedMarch 31, 2017 are as follows:

	Number of restricted stock shares		Weighted average grant date fair value
Unvested at beginning of period	288,964			$	34.94
Granted	—			—
Vested	(69,439	)		34.87
Forfeited/cancelled	—			—
Unvested at end of period	219,525			$	34.96