Accounting Standards and Significant Accounting Policies - Schedule of Impact of New Accounting Pronouncements (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended			6 Months Ended
	Jul. 31, 2018	Jul. 31, 2017		Jul. 31, 2018	Jul. 31, 2017		Jan. 31, 2018
Revenue:
Subscription	$ 87,854	$ 55,317	[1]	$ 164,695	$ 103,596	[1]
Professional services and other	6,732	4,942	[1]	13,512	8,988	[1]
Total revenue	94,586	60,259	[1]	178,207	112,584	[1]
Gross profit	66,358	40,577	[1]	125,872	75,439	[1]
Operating expenses:
Sales and marketing	59,004	37,891	[1]	108,497	73,194	[1]
Total operating expenses	104,788	66,762	[1]	189,280	129,063	[1]
Loss before provision for (benefit from) income taxes	(40,192)	(25,803)	[1]	(66,385)	(53,261)	[1]
Net loss	$ (39,207)	$ (26,032)	[1],[2]	$ (65,169)	$ (53,738)	[1],[3]
Net loss per share, basic and diluted (in dollars per share)	$ (0.37)	$ (0.28)	[1]	$ (0.62)	$ (0.80)	[1]
Current assets:
Deferred commissions	$ 19,848			$ 19,848			$ 17,755	[4]
Prepaid expenses and other current assets	17,433			17,433			17,781	[4]
Total current assets	633,376			633,376			317,498	[4]
Deferred commissions, noncurrent	43,287			43,287			40,755	[4]
Total assets	763,917			763,917			399,263	[4]
Current liabilities:
Deferred revenue	186,427			186,427			159,816	[4]
Total current liabilities	218,140			218,140			187,943	[4]
Deferred revenue, noncurrent	5,471			5,471			4,963	[4]
Total liabilities	518,772			518,772			199,923	[4]
Accumulated deficit	(431,883)			(431,883)			(366,714)	[4]
Total stockholders’ equity	245,145			245,145			199,340	[4]
Total liabilities and stockholders’ equity	$ 763,917			$ 763,917			399,263	[4]
As Reported
Revenue:
Subscription		$ 56,080			$ 104,437
Professional services and other		4,915			9,565
Total revenue		60,995			114,002
Gross profit		41,313			76,857
Operating expenses:
Sales and marketing		39,597			76,777
Total operating expenses		68,468			132,646
Loss before provision for (benefit from) income taxes		(26,773)			(55,426)
Net loss		$ (27,002)			$ (55,903)
Net loss per share, basic and diluted (in dollars per share)		$ (0.29)			$ (0.83)
Current assets:
Deferred commissions							16,481
Prepaid expenses and other current assets							16,973
Total current assets							315,416
Deferred commissions, noncurrent							10,971
Total assets							367,397
Current liabilities:
Deferred revenue							162,633
Total current liabilities							190,760
Deferred revenue, noncurrent							6,034
Total liabilities							203,811
Accumulated deficit							(402,468)
Total stockholders’ equity							163,586
Total liabilities and stockholders’ equity							367,397
Accounting Standards Update 2014-09 | Adjustments
Revenue:
Subscription		$ (763)			$ (841)
Professional services and other		27			(577)
Total revenue		(736)			(1,418)
Gross profit		(736)			(1,418)
Operating expenses:
Sales and marketing		(1,706)			(3,583)
Total operating expenses		(1,706)			(3,583)
Loss before provision for (benefit from) income taxes		970			2,165
Net loss		$ 970			$ 2,165
Net loss per share, basic and diluted (in dollars per share)		$ 0.01			$ 0.03
Current assets:
Deferred commissions							1,274
Prepaid expenses and other current assets							808
Total current assets							2,082
Deferred commissions, noncurrent							29,784
Total assets							31,866
Current liabilities:
Deferred revenue							(2,817)
Total current liabilities							(2,817)
Deferred revenue, noncurrent							(1,071)
Total liabilities							(3,888)
Accumulated deficit							35,754
Total stockholders’ equity							35,754
Total liabilities and stockholders’ equity							$ 31,866

[1] See Note 2 for a summary of adjustments.

[2] See Note 2 for a summary of adjustments.

[3] See Note 2 for a summary of adjustments.

[4] See Note 2 for a summary of adjustments.