Fair Value Measurements - Summary of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Jan. 31, 2018	Jan. 31, 2017
Schedule of Available-for-Sale Securities [Line Items]
Amortized Cost	$ 52,146	$ 38,540
Gross Unrealized Gains	9	14
Gross Unrealized Losses	(63)	(8)
Estimated Fair Value	52,092	38,546
Cash [Member]
Schedule of Available-for-Sale Securities [Line Items]
Amortized Cost	39,084	25,576
Estimated Fair Value	39,084	25,576
Cash Equivalents [Member]
Schedule of Available-for-Sale Securities [Line Items]
Amortized Cost	4,568	2,726
Estimated Fair Value	4,568	2,726
Cash and Cash Equivalents [Member]
Schedule of Available-for-Sale Securities [Line Items]
Amortized Cost	43,652	28,302
Estimated Fair Value	43,652	28,302
U.S. Treasury Notes and Bonds - Short Term [Member]
Schedule of Available-for-Sale Securities [Line Items]
Amortized Cost	2,001	4,248
Gross Unrealized Gains		5
Gross Unrealized Losses	(8)
Estimated Fair Value	1,993	4,253
U.S. Treasury Notes and Bonds - Long Term [Member]
Schedule of Available-for-Sale Securities [Line Items]
Amortized Cost	1,740	2,003
Gross Unrealized Losses	(16)	(6)
Estimated Fair Value	1,724	1,997
U.S. Government Agency Issues Short Term [Member]
Schedule of Available-for-Sale Securities [Line Items]
Amortized Cost	1,991	991
Gross Unrealized Gains	9	9
Gross Unrealized Losses	(2)
Estimated Fair Value	1,998	1,000
U.S. Government Agency Issues Long Term [Member]
Schedule of Available-for-Sale Securities [Line Items]
Amortized Cost	1,002	2,996
Gross Unrealized Losses	(17)	(2)
Estimated Fair Value	985	$ 2,994
Corporate Bonds Long Term [Member]
Schedule of Available-for-Sale Securities [Line Items]
Amortized Cost	1,760
Gross Unrealized Losses	(20)
Estimated Fair Value	$ 1,740