Net income per share attributable to common stockholders - Basic and Diluted Net Income per Share Attributable to Common Stockholders (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Numerator:
Allocation of net income	$ 16,752us-gaap_NetIncomeLoss	$ 11,049us-gaap_NetIncomeLoss
Less: net income allocable to participating securities	0	(3,040)
Net income attributable to common stockholders—basic	16,752us-gaap_UndistributedEarnings	8,009us-gaap_UndistributedEarnings
Add: net income allocable to dilutive participating securities	0	443
Net income attributable to common stockholders—diluted	16,752us-gaap_UndistributedEarningsDiluted	8,452us-gaap_UndistributedEarningsDiluted
Denominator:
Weighted-average common shares—basic (in shares)	132,278	81,582
Weighted-average common shares—diluted (in shares)	148,573	100,783
Net income per share attributable to common stockholders - Basic (in dollars per share)	$ 0.13us-gaap_EarningsPerShareBasic	$ 0.10us-gaap_EarningsPerShareBasic
Net income per share attributable to common stockholders - Diluted (in dollars per share)	$ 0.11us-gaap_EarningsPerShareDiluted	$ 0.08us-gaap_EarningsPerShareDiluted
Class A [Member]
Numerator:
Allocation of net income	8,926
Less: net income allocable to participating securities	0
Net income attributable to common stockholders—basic	8,926
Add: net income allocable to dilutive participating securities	0
Reallocation of net income	7,826
Net income attributable to common stockholders—diluted	16,752
Denominator:
Weighted-average common shares—basic (in shares)	70,483
Conversion of Class B to Class A common stock outstanding (in shares)	61,795
Effect of potentially dilutive stock options, ESPP shares and RSUs (in shares)	16,295
Weighted-average common shares—diluted (in shares)	148,573
Net income per share attributable to common stockholders - Basic (in dollars per share)	$ 0.13
Net income per share attributable to common stockholders - Diluted (in dollars per share)	$ 0.11
Class B [Member]
Numerator:
Allocation of net income	7,826
Less: net income allocable to participating securities	0
Net income attributable to common stockholders—basic	7,826
Add: net income allocable to dilutive participating securities	0
Reallocation of net income	968
Net income attributable to common stockholders—diluted	8,794
Denominator:
Weighted-average common shares—basic (in shares)	61,795
Conversion of Class B to Class A common stock outstanding (in shares)	0
Effect of potentially dilutive stock options, ESPP shares and RSUs (in shares)	16,202
Weighted-average common shares—diluted (in shares)	77,997
Net income per share attributable to common stockholders - Basic (in dollars per share)	$ 0.13
Net income per share attributable to common stockholders - Diluted (in dollars per share)	$ 0.11
Common [Member]
Numerator:
Allocation of net income		11,049
Less: net income allocable to participating securities		(3,040)
Net income attributable to common stockholders—basic		8,009
Add: net income allocable to dilutive participating securities		443
Net income attributable to common stockholders—diluted		$ 8,452
Denominator:
Weighted-average common shares—basic (in shares)		81,582
Conversion of Class B to Class A common stock outstanding (in shares)		0
Effect of potentially dilutive stock options, ESPP shares and RSUs (in shares)		19,201
Weighted-average common shares—diluted (in shares)		100,783
Net income per share attributable to common stockholders - Basic (in dollars per share)		$ 0.10
Net income per share attributable to common stockholders - Diluted (in dollars per share)		$ 0.08

Net income per share attributable to common stockholders - Basic and Diluted Net Income per Share Attributable to Common Stockholders (Details) (USD $)
In Thousands, except Per Share data, unless otherwise specified