Note 7. Stock-Based Compensation

The expense relating to stock options is recognized on a straight-line basis over the requisite service period, usually the vesting period, based on the grant-date fair value. The unamortized compensation cost, net of expected forfeitures, as of June 30, 2017 was $1.3 million related to stock options and is expected to be recognized as expense over a weighted-average period of approximately 2.0 years. The expense related to restricted stock units (RSUs) is recognized over a three-to-five year vesting period and is based on the fair value of the underlying stock on the dates of grant. The unamortized compensation cost, net of expected forfeitures, as of June 30, 2017 was $0.4 million related to RSUs and is expected to be recognized as expense over a weighted-average period of approximately 1.6 years.

For the three and six months ended June 30, 2017 and 2016, there were no excess tax benefits associated with the exercise of stock options due to the Company’s loss positions.

Valuation Assumptions

There were no stock options granted during the three months ended June 30, 2017 or the three or six months ended June 30, 2016. The fair value of the Company’s stock options granted for the three and six months ended June 30, 2017 was estimated on the grant dates using the Black-Scholes valuation option-pricing model with the following assumptions:



		Six months
		ended
		June 30, 2017
Risk-free interest rate		1.6%
Volatility		70.2%
Expected life (years)		4.0
Dividend yield		0%

The risk-free interest rate was derived from the Daily Treasury Yield Curve Rates, as published by the U.S. Department of the Treasury as of the grant date for terms equal to the expected terms of the options. The expected volatility was based on the historical volatility of the Company’s stock price over the expected term of the options. The expected term of options granted was derived from historical data based on employee exercises and post‑vesting employment termination behavior. A dividend yield of zero is applied because the Company has never paid dividends and has no intention to pay dividends in the near future.

The stock‑based compensation expense recorded is adjusted based on estimated forfeiture rates. An annualized forfeiture rate has been used as a best estimate of future forfeitures based on the Company’s historical forfeiture experience. The stock‑based compensation expense will be adjusted in later periods if the actual forfeiture rate is different from the estimate.

Common Stock Options and Restricted Stock

A summary of the option and RSU activity under the Company’s Amended and Restated 2010 Equity Incentive Plan (the Plan) is presented below (in thousands, except exercise price):


		Options outstanding
			Weighted
	Shares		Average
	Available	Number of	Exercise
	for Grant	Shares	Prices
Balance at January 1, 2017	114	522	$	13.88
Additional shares authorized under the Plan	50	—		—
Restricted stock units cancelled and returned to the Plan	5	—		—
Options granted	(1)	1	$	2.36
Options cancelled and returned to the Plan	15	(15)	$	6.94
Balance at March 31, 2017	183	508	$	14.06
Restricted stock units cancelled and returned to Plan	37	—		—
Options cancelled and returned to Plan	172	(172)	$	10.20
Balance at June 30, 2017	392	336	$	16.04

The Company also has awarded options to new employees outside of the Plan and may continue to do so, as material inducements to the acceptance of employment with the Company, as permitted under the Listing Rules of the Nasdaq Stock Market. These grants must be approved by the compensation committee of the board of directors, a majority of the independent directors or, below a specified share level, by an authorized executive officer.

A summary of RSU activity under the Plan is presented below (in thousands, except for fair value):


		Weighted
		Average
	Number of	Grant-Date
	Shares	Fair Value
Non-vested shares at January 1, 2017	148	$	8.13
Vested	(54)	$	11.64
Cancelled	(5)	$	5.30
Non-vested shares at March 31, 2017	89	$	6.16
Cancelled	(37)	$	5.75
Non-vested shares at June 30, 2017	52	$	6.46

In the quarter ended March 31, 2017, the Company paid approximately $22,000 for employee income taxes related to net share settlement of vested RSUs.

The total intrinsic value of the RSUs outstanding as of June 30, 2017 was $0.1 million.

The following table summarizes significant ranges of outstanding and exercisable options as of June 30, 2017 (in thousands, except contractual life and exercise price):


	Options Outstanding				Options Exercisable
		Weighted
		Average
		Remaining	Weighted			Weighted
		Contractual	Average			Average		Aggregate
	Number	Life	Exercise		Number	Exercise		Intrinsic
Range of Exercise Price	Outstanding	(in Years)	Price		Exercisable	Price		value
$2.36 - $7.19	29	6.86	$	5.15	12	$	5.30
$7.20 - $16.99	174	7.35	$	7.20	73	$	7.20
$17.00 - $20.49	6	2.69	$	17.00	6	$	17.00
$20.50 - $30.89	54	6.94	$	20.50	45	$	20.50
$30.90 - $46.19	67	1.94	$	36.44	67	$	36.44
$46.20 - $54.30	6	0.47	$	51.45	6	$	51.50
$2.36 - $54.30	336	6.12	$	16.04	209	$	20.95	$	—
Vested and expected to vest	323	5.81	$	16.38				$	—
Exercisable	209	4.35	$	20.95				$	—

There were no stock options exercised during the six months ended June 30, 2017 or 2016.

Employee Stock Purchase Plan

In June 2010, the Company’s stockholders approved the 2010 Employee Stock Purchase Plan (ESPP). A total of 2,000,000 shares of common stock were initially reserved for issuance under the ESPP in 2010. On September 1, 2010, the Company commenced the first offering period under the ESPP. In May 2015, the Company’s stockholders approved an amendment increasing the number of shares reserved for issuance by 2,000,000 shares. The ESPP, which is intended to qualify under Section 423 of the Internal Revenue Code, is administered by the board of directors or the compensation committee of the board of directors. The ESPP provides that eligible employees may purchase up to $25,000 worth of the Company’s common stock annually over the course of two six-month offering periods. The purchase price to be paid by participants is 85% of the price per share of the Company’s common stock either at the beginning or the end of each six-month offering period, whichever is less.

In February 2017, the Compensation Committee of the Board of Directors elected to suspend the ESPP plan. ESPP Plan participants were refunded their payroll contributions for the then open purchase period