Cash Equivalents and Short-term Investments - Schedule of Amortized Costs, Unrealized Gains and Losses and Estimated Fair Value of Cash Equivalents and Short-term Investments (Details) - USD ($) $ in Thousands	Apr. 30, 2017	Jan. 31, 2017
Investments:
Investments, amortized cost	$ 2,500	$ 14,380
Investments, estimated fair value	2,500	14,390
Total short-term investments, amortized cost	2,500	14,380
Total short-term investments, unrealized gain	0	13
Total short-term investments, unrealized loss	0	(3)
Total short-term investments, estimated fair value	2,500	14,390
Amortized cost	220,151	24,945
Estimated fair value	220,151	24,955
Asset-backed securities
Investments:
Investments, amortized cost		1,538
Investments, unrealized gain		0
Investments, unrealized loss		0
Investments, estimated fair value		1,538
Corporate debt securities
Investments:
Investments, amortized cost	2,500	12,842
Investments, unrealized gain	0	13
Investments, unrealized loss	0	(3)
Investments, estimated fair value	2,500	12,852
Money market funds
Cash equivalents:
Cash equivalents, amortized cost	217,651	10,565
Cash equivalents, estimated fair value	$ 217,651	$ 10,565