Stock-Based Awards

6 Months Ended

Jun. 30, 2020

Share-based Payment Arrangement [Abstract]

The Company grants stock-based awards under its 2017 Stock Option and Incentive Plan (the 2017 Plan) and is authorized to issue common stock under its 2017 Employee Stock Purchase Plan (ESPP). The Company also has outstanding stock options under its 2015 Equity Incentive Plan but is no longer granting awards under this plan. As of June 30, 2020, 1,608,183 shares of common stock were available for issuance under the 2017 Plan. As of June 30, 2020, 1,409,433 shares of common stock were available for issuance to participating employees under the ESPP. The purchase price of common stock under the Company's 2017 ESPP, is equal to 85% of the lesser of (i) the fair market value per share of the common stock on the first business day of an offering period and (ii) the fair market value per share of the common stock on the purchase date. The fair value of the discounted purchases made under the Company's 2017 ESPP is calculated using the Black-Scholes valuation model. The fair value of the look-back provision plus the 15% discount is recognized as stock-based compensation expense in the consolidated statements of operations and comprehensive loss over the 6-month purchase period. Employees began participating in the ESPP program during the second quarter of 2020.

Stock-based compensation expense was classified in the consolidated statements of operations and comprehensive loss as follows:


	Three Months Ended June 30,						Six Months Ended June 30,
(in thousands)	2020		2019		2020		2019
Research and development expenses	$	5,293	$	1,790	$	8,564	$	3,482
Selling, general, and administrative expenses	5,316		2,317		9,039		6,854
Total stock-based compensation	$	10,609	$	4,107	$	17,603	$	10,336

As of June 30, 2020, total unrecognized compensation cost related to the unvested share-based awards was $105.0 million, which is expected to be recognized over a weighted average of 2.8 years.

During the six months ended June 30, 2019, the Company recorded $2.4 million of stock-based compensation expense related to the modification of stock options pursuant to the transition agreement with its former President and Chief Executive

Officer. These expenses were classified as selling, general, and administrative expenses within the consolidated statements of operations and comprehensive loss.

During the three and six months ended June 30, 2020, the Company recorded $1.3 million of stock-based compensation expense related to vesting events associated with performance-based restricted stock units that became probable and were achieved during the second quarter of 2020. These expenses were classified as research and development expenses within the consolidated statements of operations and comprehensive loss.