As part of the Series D and E Convertible Preferred share investment agreements, the investors received warrants to purchase ordinary shares. The Company accounted for these warrants as equity instruments based on the guidance of ASC 815, "Derivatives and Hedging," ASC 480-10, "Distinguishing Liabilities from Equity," its related FASB staff positions, ASC 815-40 "Contracts in Entity’s Own Stock" and the AICPA Technical Practice Aid for accounting for preferred shares and warrants, including the roadmap for accounting for freestanding financial instruments indexed to, and potentially settled in, a company’s own stock.

In the years ended December 31, 2018 and 2017, warrants to purchase 504,225 and 1,418,711 ordinary shares, respectively, were cashlessly exercised, resulting in the issuance of 437,081 and 803,138 ordinary shares, respectively. Also, in the year ended December 31, 2018 and 2017 warrants to purchase 3,879 and 6,498 ordinary shares, respectively, with an exercise price of $3.59 per share were exercised for cash. No warrants were outstanding as of December 31, 2019 and 2018.

Until the IPO in October 2015, the Company maintained and granted option awards under the 2003 Share Option Plan (the "2003 Plan") and the 2013 Equity Incentive Share Option Plan (the "2013 Plan") for the Company’s officers, directors, employees and advisors. The 2003 Plan and the 2013 Plan terminated as of the IPO as to future awards, but they continue to govern option awards previously granted thereunder.

In September 2015, the Company adopted the 2015 Omnibus Incentive Plan (the "2015 Plan"). The Company’s shareholders approved the 2015 Plan in September 2015. Under the 2015 Plan, the Company can issue various types of equity compensation awards such as restricted shares, performance shares, restricted stock units ("RSUs"), performance units, long-term cash award and other share-based awards. Options granted under the 2015 Plan generally have a four-year vesting period and expire ten years after the date of grant. Options granted under the 2015 Plan that are cancelled or forfeited before expiration become available for future grants. RSUs granted under the 2015 Plan vest in equal installments over a three-year period.

On December 31, 2019, in accordance with the terms of the 2015 Plan, the number of shares available for issuance under the 2015 Plan automatically increased by 4% of the Company’s outstanding ordinary shares as of December 30, 2019. As a result, the number of shares available for issuance under the 2015 Plan increased from 27,035,515 shares to 31,015,695 shares. As of December 31, 2019, 15,826,518 ordinary shares are available for grant under the 2015 Plan.

In September 2015, the Company adopted an ESPP to encourage and enable eligible employees to acquire ownership of the Company’s ordinary shares purchased through accumulated payroll deductions on an after-tax basis. The ESPP is intended to be an "employee stock purchase plan" within the meaning of Section 423 of the Code and the provisions of the ESPP will be construed in a manner consistent with the requirements of such section. The Company began its offerings under the ESPP on August 1, 2016. The Company issued 414,559 ordinary shares for the plan periods ended through December 31, 2019.

On December 31, 2019, in accordance with the terms of the ESPP, the number of shares available for purchase by eligible employees who participate in the ESPP automatically increased by 1% of the Company’s outstanding ordinary shares outstanding on December 30, 2019. As of December 31, 2019, 4,050,089 ordinary shares are available for offering under the ESPP.

The fair value of share-based awards was estimated using the Black-Scholes model for all equity grants. For market condition awards, the Company also applied the Monte-Carlo simulation model, with the following underlying assumptions:


	Year ended December 31,
	2019		2018		2017
Stock Option Plans
Expected term (years)	5.50-6.00		5.50-6.25		5.50-6.25
Expected volatility	55%-61%		52%-55%		57%-59%
Risk-free interest rate	1.73%-2.40%		2.70%-2.99%		1.97%-2.23%
Dividend yield	0.00	%	0.00	%	0.00	%
ESPP
Expected term (years)	0.50		0.50		0.50
Expected volatility	44%-62%		45%-53%		76%-82%
Risk-free interest rate	2.10%-2.51%		1.61%-2.14%		0.62%-1.13%
Dividend yield	0.00	%	0.00	%	0.00	%

A summary of the status of the Company’s options to purchase ordinary shares as of December 31, 2019 and changes during the year ended on that date is presented below:


	Year ended December 31, 2019
	Number of options	Weighted average exercise price		Aggregate intrinsic value
Outstanding at beginning of year	14,438,215	$	13.56
Granted	1,552,987	50.45
Exercised	(5,466,170)	10.83
Forfeited and cancelled	(174,222)	22.11
Outstanding at end of year	10,350,810	$	20.40	$	661,150
Exercisable options	3,217,923	$	15.55	$	221,146


	Year ended December 31, 2019
	Number of RSUs	Weighted average grant date fair value price		Aggregate intrinsic value
Unvested at beginning of year	1,613,197	$	14.04
Granted	634,694	52.28
Vested	(740,714)	13.47
Forfeited and cancelled	(32,782)	37.84
Unvested at end of year	1,474,395	$	30.26	$	124,247

The total equity-based compensation expense related to all of the Company’s equity-based awards recognized for the years ended December 31, 2019, 2018 and 2017, was comprised as follows:


	Year ended December 31,
	2019		2018		2017
Cost of revenues	$	2,231	$	1,261	$	467
Research, development and clinical trials	7,570		4,709		3,587
Sales and marketing	11,897		7,393		3,784
General and administrative	30,718		26,483		19,278
Total share-based compensation expense	$	52,416	$	39,846	$	27,116

As of December 31, 2019, unamortized share-based compensation costs amounted to $62,498 and are expected to be recognized over a weighted average period of approximately 2.51 years.

The weighted average grant date exercise price of the Company’s options granted during the years ended December 31, 2019, 2018 and 2017 were $50.45, $23.73 and $10.53 per share, respectively.

The weighted average grant date fair values of the Company’s options forfeited and cancelled during the years ended December 31, 2019, 2018 and 2017 were $22.11, $15.09 and $12.54, respectively.

The aggregate intrinsic values for the options exercised during the years ended December 31, 2019, 2018 and 2017 were $266,626, $57,813 and $17,945, respectively. The aggregate intrinsic value is calculated as the difference between the per share exercise price and the deemed fair value of the Company’s ordinary shares for each share subject to an option multiplied by the number of shares subject to options at the date of exercise. The Company deemed the fair value of the Company’s ordinary shares to be $84.27, $33.48 and $20.20 per share as of December 31, 2019, 2018, and 2017, respectively.


Exercise price	Number of options outstanding	Weighted average remaining contractual term	Number of options exercisable	Weighted average remaining contractual term
$		(years)		(years)
0.23 - 10.00	2,256,916	6.15	984,380	4.87
10.01 - 20.00	3,205,758	6.83	869,058	5.84
20.01 - 30.00	2,933,518	7.4	1,225,951	6.57
30.01 - 40.00	424,414	8.56	138,534	8.47
40.01 - 50.00	1,347,064	9.29	—	—
50.01 - 60.00	44,380	9.39	—	—
60.01 - 90.00	138,760	9.7	—	—
	10,350,810	7.28	3,217,923	5.94