Fair Value Measurements - Schedule of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Jan. 31, 2018	Jan. 31, 2017
Assets:
Cash equivalents, fair value	$ 90,770	$ 10,565
Money market funds
Assets:
Cash equivalents, fair value	90,770
Fair Value, Measurements, Recurring
Assets:
Cash equivalents, fair value	90,770	10,565
Short term investments, fair value	101,765	14,390
Total cash equivalents and short-term investments	192,535	24,955
Liabilities:
Series B redeemable convertible preferred stock warrant		304
Fair Value, Measurements, Recurring | Level 1
Assets:
Cash equivalents, fair value	90,770	10,565
Short term investments, fair value	0	0
Total cash equivalents and short-term investments	90,770	10,565
Liabilities:
Series B redeemable convertible preferred stock warrant		0
Fair Value, Measurements, Recurring | Level 2
Assets:
Cash equivalents, fair value	0	0
Short term investments, fair value	101,765	14,390
Total cash equivalents and short-term investments	101,765	14,390
Liabilities:
Series B redeemable convertible preferred stock warrant		0
Fair Value, Measurements, Recurring | Level 3
Assets:
Cash equivalents, fair value	0	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	15,946
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	15,946
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	61,738
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	61,738
Fair Value, Measurements, Recurring | U.S. treasury securities | Level 3
Assets:
Short term investments, fair value	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 | Corporate debt securities
Assets:
Short term investments, fair value	24,081	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	24,081	12,852
Fair Value, Measurements, Recurring | Corporate debt securities | Level 3
Assets:
Short term investments, fair value	0	0
Fair Value, Measurements, Recurring | Money market funds
Assets:
Cash equivalents, fair value	90,770	10,565
Fair Value, Measurements, Recurring | Money market funds | Level 1
Assets:
Cash equivalents, fair value	90,770	10,565
Fair Value, Measurements, Recurring | Money market funds | Level 2
Assets:
Cash equivalents, fair value	0	0
Fair Value, Measurements, Recurring | Money market funds | Level 3
Assets:
Cash equivalents, fair value	$ 0	$ 0