Fair Value Measurements - Schedule of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Jul. 31, 2017	Jan. 31, 2017
Assets:
Fair value, cash equivalents	$ 115,511	$ 10,565
Money market funds
Assets:
Fair value, cash equivalents	95,495
Commercial paper
Assets:
Fair value, cash equivalents	15,020
U.S. treasury securities
Assets:
Fair value, cash equivalents	4,996
Fair Value, Measurements, Recurring
Assets:
Fair value, cash equivalents	115,511	10,565
Short term investments, fair value	86,755	14,390
Total cash equivalents and short-term investments	202,266	24,955
Liabilities:
Series B redeemable convertible preferred stock warrant		304
Fair Value, Measurements, Recurring | Level 1
Assets:
Fair value, cash equivalents	95,495	10,565
Short term investments, fair value	0	0
Total cash equivalents and short-term investments	95,495	10,565
Liabilities:
Series B redeemable convertible preferred stock warrant		0
Fair Value, Measurements, Recurring | Level 2
Assets:
Fair value, cash equivalents	20,016
Short term investments, fair value	86,755	14,390
Total cash equivalents and short-term investments	106,771	14,390
Liabilities:
Series B redeemable convertible preferred stock warrant		0
Fair Value, Measurements, Recurring | Level 3
Assets:
Fair value, cash equivalents	0
Short term investments, fair value	0	0
Total cash equivalents and short-term investments	0	0
Liabilities:
Series B redeemable convertible preferred stock warrant		304
Fair Value, Measurements, Recurring | Commercial paper
Assets:
Short term investments, fair value	18,913
Fair Value, Measurements, Recurring | Commercial paper | Level 1
Assets:
Short term investments, fair value	0
Fair Value, Measurements, Recurring | Commercial paper | Level 2
Assets:
Short term investments, fair value	18,913
Fair Value, Measurements, Recurring | Commercial paper | Level 3
Assets:
Short term investments, fair value	0
Fair Value, Measurements, Recurring | U.S. treasury securities
Assets:
Short term investments, fair value	45,081
Fair Value, Measurements, Recurring | U.S. treasury securities | Level 1
Assets:
Short term investments, fair value	0
Fair Value, Measurements, Recurring | U.S. treasury securities | Level 2
Assets:
Short term investments, fair value	45,081
Fair Value, Measurements, Recurring | U.S. treasury securities | Level 3
Assets:
Short term investments, fair value	0
Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Short term investments, fair value	22,761	12,852
Fair Value, Measurements, Recurring | Corporate debt securities | Level 1
Assets:
Short term investments, fair value	0	0
Fair Value, Measurements, Recurring | Corporate debt securities | Level 2
Assets:
Short term investments, fair value	22,761	12,852
Fair Value, Measurements, Recurring | Corporate debt securities | Level 3
Assets:
Short term investments, fair value	0	0
Fair Value, Measurements, Recurring | Asset-backed securities
Assets:
Short term investments, fair value		1,538
Fair Value, Measurements, Recurring | Asset-backed securities | Level 1
Assets:
Short term investments, fair value		0
Fair Value, Measurements, Recurring | Asset-backed securities | Level 2
Assets:
Short term investments, fair value		1,538
Fair Value, Measurements, Recurring | Asset-backed securities | Level 3
Assets:
Short term investments, fair value		0
Fair Value, Measurements, Recurring | Money market funds
Assets:
Fair value, cash equivalents	95,495
Fair Value, Measurements, Recurring | Money market funds | Level 1
Assets:
Fair value, cash equivalents	95,495
Fair Value, Measurements, Recurring | Money market funds | Level 2
Assets:
Fair value, cash equivalents	0	0
Fair Value, Measurements, Recurring | Money market funds | Level 3
Assets:
Fair value, cash equivalents	0	$ 0
Fair Value, Measurements, Recurring | Commercial paper
Assets:
Fair value, cash equivalents	15,020
Fair Value, Measurements, Recurring | Commercial paper | Level 1
Assets:
Fair value, cash equivalents	0
Fair Value, Measurements, Recurring | Commercial paper | Level 2
Assets:
Fair value, cash equivalents	15,020
Fair Value, Measurements, Recurring | Commercial paper | Level 3
Assets:
Fair value, cash equivalents	0
Fair Value, Measurements, Recurring | U.S. treasury securities
Assets:
Fair value, cash equivalents	4,996
Fair Value, Measurements, Recurring | U.S. treasury securities | Level 1
Assets:
Fair value, cash equivalents	0
Fair Value, Measurements, Recurring | U.S. treasury securities | Level 2
Assets:
Fair value, cash equivalents	4,996
Fair Value, Measurements, Recurring | U.S. treasury securities | Level 3
Assets:
Fair value, cash equivalents	$ 0