Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of stock option activity

The following table summarizes the activity for all stock options under all of the Company’s equity incentive plans for the years ended December 31, 2018 and 2017 (shares and aggregate intrinsic value in thousands):

	Number of Options		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life	Aggregate Intrinsic Value
Outstanding at December 31, 2016	12,897		$	5.94	7.49	$	9,625
Granted	5,266		5.17
Exercised	(687	)	2.96
Cancelled	(1,208	)	7.62
Outstanding at December 31, 2017	16,268		5.70		7.41	$	14,832
Granted	1,529		8.63
Exercised	(3,271	)	5.23
Cancelled	(936	)	6.63
Outstanding at December 31, 2018	13,590		$	6.07	6.63	$	66,462
Options vested and exercisable at December 31, 2018	7,974		$	5.64	5.52	$	42,504
Options vested and expected to vest at December 31, 2018	13,590		$	6.07	6.63	$	66,462

Estimated fair value of stock options

The Company estimated the fair value of stock options with the following assumptions:

	Year Ended December 31,
	2018		2017		2016
Risk-free interest rate	2.72% - 2.92%		1.88% - 2.22%		1.18% - 2.23%
Volatility	44.87% - 54.61%		45.95% - 50.52%		36.00% - 49.64%
Expected term (in years)	6.09 - 6.11		5.94 - 6.08		5.00 - 6.26
Expected dividend yield	0.00	%	0.00	%	0.00	%

Summary of activity for all RSUs

The following table summarizes the activity for all RSUs under all of the Company’s equity incentive plans for the years ended December 31, 2018 and 2017 (shares in thousands):

	Shares		Weighted Average Grant Date Fair Value
Unvested balance at December 31, 2016	4,106		$	6.87
Granted	3,540		5.30
Issued	(1,115	)	7.36
Cancelled / forfeited	(1,201	)	5.81
Unvested balance at December 31, 2017	5,330		5.82
Granted	2,019		8.75
Issued	(1,720	)	6.36
Cancelled / forfeited	(1,447	)	5.75
Unvested balance at December 31, 2018	4,182		$	7.05

Summary of stock-based compensation expense

The Company recognized stock-based compensation expense, including ESPP expenses, in the consolidated statements of operations as follows (in thousands): 

	Year Ended December 31,
	2018		2017		2016
Cost of customer agreements and incentives	$	2,568	$	2,299	$	2,039
Cost of solar energy systems and product sales	718		609		409
Sales and marketing	7,191		5,196		7,831
Research and development	1,253		836		515
General and administration	16,126		13,102		7,929
Total	$	27,856	$	22,042	$	18,723