Equity Award Plans (Tables)

12 Months Ended

Dec. 31, 2015

A summary of stock option activity is as follows (in thousands, except per share amounts):

						Weighted-
				Weighted-		Average
				Average		Remaining		Aggregate
	Stock			Exercise		Contractual		Intrinsic
	Options			Price		Term (Years)		Value
Outstanding - January 1, 2013		14,903		$	4.80		7.67	$	107,653
Granted (weighted-average fair value of $27.55)		4,364			39.02
Issued in connection with a business acquisition (weighted-average fair value of $49.13)		303			1.97
Exercised		(4,260	)		3.65				149,653
Canceled		(1,361	)		15.30
Outstanding - December 31, 2013		13,949			14.77		7.52		586,740
Granted (weighted-average fair value of $47.45)		5,544			65.69
Exercised		(3,176	)		6.38				185,822
Canceled		(2,367	)		38.51
Outstanding - December 31, 2014		13,950			32.89		7.64		342,293
Granted (weighted-average fair value of $31.24)		6,448			49.67
Exercised		(951	)		12.25				37,929
Canceled		(1,132	)		56.07
Outstanding - December 31, 2015		18,315		$	38.43		7.74	$	293,855
Options vested and exercisable - December 31, 2013		6,696		$	4.62		6.54	$	349,523
Options vested and exercisable - December 31, 2014		6,537		$	12.72		6.30	$	272,140
Options vested and exercisable - December 31, 2015		8,029		$	21.53		5.88	$	258,310
Options vested and expected to vest - December 31, 2013		12,828		$	13.53		7.41	$	555,412
Options vested and expected to vest - December 31, 2014		12,423		$	30.15		7.46	$	333,813
Options vested and expected to vest - December 31, 2015		15,184		$	35.94		7.37	$	287,673

The fair values were estimated on each grant date with the following weighted-average assumptions:

	Year Ended December 31,
	2015			2014			2013
Dividend yield		0	%		0	%		0	%
Annual risk-free rate of return		2.14	%		1.95	%		1.45	%
Expected volatility		65.76	%		83.66	%		92.86	%
Expected term (years)		7.02			6.25			6.06

A summary of RSU activity is as follows (in thousands, except per share amounts):

The amount of stock-based compensation expense that was capitalized is as follows (in thousands):

	Year Ended December 31,
	2015		2014		2013
Capitalized under:
Inventories	$	226	$	192	$	433
Other assets	$	3,136	$	142	$	—
Property, plant and equipment - net	$	2,997	$	5,340	$	—
Solar energy systems, leased and to be leased - net	$	24,075	$	17,700	$	6,576

Stock-based compensation expense was included in cost of revenue and operating expenses as follows (in thousands):