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, as of September 30, 2019, was $0.2 million related to stock options and is expected to be recognized as expense over a weighted-average period of approximately 2.2 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, as of September 30, 2019, was $0.3 million related to RSUs and is expected to be recognized as expense over a weighted-average period of approximately 2.3 years.

For the three and nine months ended September 30, 2019 and 2018, there were no excess tax benefits associated with the exercise of stock options due to the Company’s historical loss positions.

The fair value of the Company’s stock options granted during the nine months ended September 30, 2019 and 2018 was estimated on the grant dates using the Black-Scholes valuation option-pricing model with the following assumptions:

There were no awards granted during the three months ended September 30, 2019 and 2018. 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.

Prior to January 1, 2019, the stock‑based compensation expense recorded was 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. Stock‑based compensation expense was then adjusted in later periods if the actual forfeiture rate is different from the estimate. Upon the adoption of ASU No. 2016-09 on January 1, 2019, the Company changed its accounting policy and began accounting for forfeitures as they occur. Historically, estimated forfeitures were immaterial to the condensed consolidated financial statements.

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

				Options outstanding
							Weighted
	Shares						Average
	Available			Number of			Exercise
	for Grant			Shares			Prices
Balance as of January 1, 2019		200			17		$	83.80
Additional shares authorized under the Plan		2			—			—
RSUs granted		(101	)		—			—
RSUs cancelled and returned to the Plan		1			—			—
Options granted		(65	)		65		$	4.00
Balance as of March 31, 2019		37			82		$	20.40
RSUs granted		(6	)		—			—
Options cancelled and returned to the Plan		1			(1	)	$	144.00
Balance as of June 30, 2019		32			81		$	20.00
Plan termination		(32	)		—		$	—
Balance as of September 30, 2019		-			81		$	20.00

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 as of January 1, 2019		14		$	24.60
Granted		101		$	4.00
Vested		(8	)	$	29.60
Cancelled		(1	)	$	25.20
Non-vested shares as of March 31, 2019		106		$	4.60
Granted		6		$	4.60
Vested		(5	)	$	16.20
Non-vested shares as of June 30, 2019		107		$	4.00
Vested		(16	)	$	4.00
Non-vested shares as of September 30, 2019		91		$	4.00

The total intrinsic value of the RSUs outstanding as of September 30, 2019 was $0.2 million.

In August 2019, the Company’s stockholders approved the 2019 Stock Incentive Plan (the 2019 Plan), and, as a result, the 2010 Plan was automatically terminated. No future grants of awards will be made under the 2010 Plan, although it will continue to govern prior awards granted thereunder, until all such awards granted have been exercised, forfeited, canceled, expired or otherwise terminated in accordance with the terms of such grants. The 2019 Plan authorizes the board of directors or the compensation committee of the board of directors to grant a broad range of awards including stock options, stock appreciation rights, restricted stock, performance-based awards, and restricted stock units. Under the 2019 Plan, 182,500 shares have been reserved for issuance.

The term of all incentive stock options granted to a person who, at the time of grant, owns stock representing more than 10% of the voting power of all classes of the Company’s stock may not exceed five years. The exercise price of stock options granted under the 2019 Plan must be at least equal to the fair market value of the shares on the date of grant. Generally, options granted under the 2019 Plan will vest over a three to four-year period and have a term of 10 years from the date of grant. In addition, the 2019 Plan provides for automatic acceleration of vesting for options granted to non-employee directors upon a change of control of the Company. As of September 30, 2019, no awards had been granted under the 2019 Plan.

The following table summarizes significant ranges of outstanding and exercisable options as of September 30, 2019 (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
$3.72 - $14.99		64		9.35	$	3.96		11	$	4.00	$	—
$15.00 - $25.59		8		4.05	$	15.00		5	$	15.00	$	—
$25.60 - $143.99		3		4.83	$	41.88		2	$	46.93	$	—
$144.00 - $409.99		5		6.90	$	144.00		5	$	144.00	$	—
$410.00 - $924.00		1		5.44	$	430.64		1	$	430.64	$	—
$3.72 - $924.00		81		8.46	$	20.36		24	$	56.81	$	—

There were no stock options exercised during the nine months ended September 30, 2019 or 2018.