Stockholder's Equity

(a) Stock Equity and Incentive Plan

The Company recognizes stock-based compensation in accordance with the provisions of ASC Topic 718, Compensation-Stock Compensation. Stock-based compensation expense, excluding compensation charges related to our employee stock purchase plan, or the ESPP, was $1,017 and $725 for the three months ended June 30, 2019 and 2018, respectively, and $1,877 and $1,568 for the six months ended June 30, 2019 and 2018, respectively. As of June 30, 2019, there was $3,676 of total unrecognized compensation expense related to stock options, which is expected to be recognized over a weighted-average period of 3.10 years. As of June 30, 2019, there was $4,654 of total unrecognized compensation expense related to restricted stock awards, which is expected to be recognized over a weighted-average period of 2.44 years.

Stock Options

During the three months ended June 30, 2019, 7 stock options were exercised for common stock. Additionally, during the three months ended June 30, 2019, 610 stock options were granted and 97 stock options expired, were canceled or were forfeited.

During the six months ended June 30, 2019, 14 stock options were exercised for common stock, $109 of which was delivered to the Company as payment for the exercise price and none of which were surrendered for minimum tax withholding obligations. Additionally, during the six months ended June 30, 2019, 610 stock options were granted with a weighted average grant date fair value of $3.09 per share and 99 stock options expired, were canceled or were forfeited. The Company has estimated the fair value of each option grant on the date of grant using the Black-Scholes option-pricing model. The weighted average assumptions utilized to determine the fair value of options granted during the six months ended June 30, 2019 and 2018 were as follows:




	Six Months Ended June 30,
	2019		2018
Risk-free interest rate	1.93	%	2.81	%
Expected volatility	36.95	%	36.60	%
Expected life (in years)	4.27		4.29
Dividend yield	0	%	0	%

As of June 30, 2019, there were 1,774 options outstanding with a weighted average exercise price of $9.92 per share and 549 options exercisable with a weighted average exercise price of $10.27 per share.

Restricted Stock

During the three months ended June 30, 2019, 199 shares of restricted stock were granted with a weighted average grant date fair value of $9.46 per share, and 20 shares of restricted stock were forfeited. Additionally, during the three months ended June 30, 2019, 63 shares of restricted stock vested, of which no shares of common stock were surrendered to the Company as payment by employees in lieu of cash to satisfy minimum tax withholding obligations in connection with the vesting of restricted stock.

During the six months ended June 30, 2019, 277 shares of restricted stock were granted with a weighted average grant date fair value of $9.78 per share and 20 shares of restricted stock were forfeited. Additionally, during the six months ended June 30, 2019, 257 shares of restricted stock vested, of which no shares of common stock were surrendered to the Company as payment by employees in lieu of cash to satisfy minimum tax withholding obligations in connection with the vesting of restricted stock.

As of June 30, 2019, there were 526 shares of restricted stock outstanding that were still subject to service-based vesting conditions.

As of June 30, 2019, the Company had no unvested outstanding options and no shares of restricted stock that were subject to performance-based or market-based vesting conditions.

(b) Employee Stock Purchase Plan

The Company's Amended and Restated 1996 Employee Stock Purchase Plan (ESPP) affords eligible employees the right to purchase common stock, via payroll deductions, through various offering periods at a purchase price equal to 85% of the fair market value of the common stock on the first or last day of the offering period, whichever is lower. During the three and six months ended June 30, 2019, 0 and 23 shares were issued under the ESPP plan, respectively. During the three and six months ended June 30, 2018, no shares were issued under the ESPP plan. The Company recorded compensation charges related to the ESPP of $16 and $14 for the three months ended June 30, 2019 and 2018, respectively, and $30 and $24 for the six months ended June 30, 2019 and 2018, respectively.

The following table presents stock-based compensation expense, including expense for the ESPP, in the Company's consolidated statements of operations for the three and six months ended June 30, 2019 and 2018:



	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Cost of product sales	$	61	$	11	$	102	$	82
Research and development	196		149		368		319
Sales, marketing and support	212		166		394		347
General and administrative	564		413		1,043		844
	$	1,033	$	739	$	1,907	$	1,592

(d) Accumulated Other Comprehensive Loss (AOCI)

Comprehensive income (loss) includes net income (loss), unrealized gains and losses from foreign currency translation, unrealized gains and losses from available for sale marketable securities and changes in fair value related to interest rate swap derivative instruments, net of tax attributes, which were not material. The components of the Company’s comprehensive income (loss) and the effect on earnings for the periods presented are detailed in the accompanying consolidated statements of comprehensive income (loss).

The balances for the three months ended June 30, 2019 and 2018 are as follows:



	Foreign Currency Translation			Unrealized Gain (Loss) on Available for Sale Marketable Securities		Interest Rate Swaps			Total Accumulated Other Comprehensive Loss
Balance, March 31, 2019	$	(13,640	)	$	—	$	(3	)	$	(13,643	)
Other comprehensive (loss) income before reclassifications	(1,332		)	—		3			(1,329		)
Reclassified from AOCI	11,483			—		—			11,483
Net other comprehensive income, June 30, 2019	10,151			—		3			10,154
Balance, June 30, 2019	$	(3,489	)	$	—	$	—		$	(3,489	)



	Foreign Currency Translation			Unrealized Gain (Loss) on Available for Sale Marketable Securities		Interest Rate Swaps			Total Accumulated Other Comprehensive Loss
Balance, March 31, 2018	$	(8,803	)	$	—	$	(47	)	$	(8,850	)
Other comprehensive (loss) income before reclassifications	(3,866		)	—		3			(3,863		)
Reclassified from AOCI	—			—		12			12
Net other comprehensive (loss) income, June 30, 2018	(3,866		)	—		15			(3,851		)
Balance, June 30, 2018	$	(12,669	)	$	—	$	(32	)	$	(12,701	)

The balances for the six months ended June 30, 2019 and 2018 are as follows:



	Foreign Currency Translation			Unrealized Gain (Loss) on Available for Sale Marketable Securities		Interest Rate Swaps			Total Accumulated Other Comprehensive Loss
Balance, December 31, 2018	$	(14,720	)	$	—	$	(11	)	$	(14,731	)
Other comprehensive (loss) income before reclassifications	(252		)	—		3			(249		)
Reclassified from AOCI	11,483			—		8			11,491
Net other comprehensive income, June 30, 2019	11,231			—		11			11,242
Balance, June 30, 2019	$	(3,489	)	$	—	$	—		$	(3,489	)



	Foreign Currency Translation			Unrealized (Loss) Gain on Available for Sale Marketable Securities			Interest Rate Swaps			Total Accumulated Other Comprehensive Loss
Balance, December 31, 2017	$	(11,247	)	$	(1	)	$	(69	)	$	(11,317	)
Other comprehensive (loss) income before reclassifications	(1,422		)	1			10			(1,411		)
Reclassified from AOCI	—			—			27			27
Net other comprehensive (loss) income, June 30, 2018	(1,422		)	1			37			(1,384		)
Balance, June 30, 2018	$	(12,669	)	$	—		$	(32	)	$	(12,701	)

For additional information, see Note 4, "Marketable Securities," and Note 17, "Derivative Instruments and Hedging Activities."