Condensed Consolidated Statements of Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Outstanding Ordinary Shares [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]
Beginning Balance, Amount at Jan. 31, 2018	$ 482,187	$ 15	$ 221,186	$ (279)	$ 261,265
Beginning Balance, Shares at Jan. 31, 2018		33,489,614
Cumulative effect of change in accounting principle	43	$ 0	0	0	43
Exercise of stock options, Amount	305	$ 0	305	0	0
Exercise of stock options, Shares		42,483
Vesting of restricted stock units, Amount	0	$ 0	0	0	0
Vesting of restricted stock units, Shares		230,240
Employee stock purchase plan, Amount	2,818	$ 0	2,818	0	0
Employee stock purchase plan, Shares		71,415
Stock repurchase, Amount	(20,624)	$ 0	(20,624)	0	0
Stock repurchase, Shares		(437,448)
Stock-based compensation expense related to stock awards granted to employees and consultants	14,195	$ 0	14,195	0	0
Net unrealized gains (losses) on investments - net of taxes	(110)	0	0	(110)	0
Net loss	(10,006)	0	0	0	(10,006)
Ending Balance, Amount at Apr. 30, 2018	468,808	$ 15	217,880	(389)	251,302
Ending Balance, Shares at Apr. 30, 2018		33,396,304
Beginning Balance, Amount at Jan. 31, 2019	$ 419,489	$ 15	188,516	97	230,861
Beginning Balance, Shares at Jan. 31, 2019	32,303,540	32,303,540
Exercise of stock options, Amount	$ 1,520	$ 0	1,520	0	0
Exercise of stock options, Shares	101,645	101,645
Vesting of restricted stock units, Amount	$ 0	$ 0	0	0	0
Vesting of restricted stock units, Shares		233,656
Employee stock purchase plan, Amount	3,063	$ 0	3,063	0	0
Employee stock purchase plan, Shares		99,759
Stock repurchase, Amount	$ 0	$ 0	0	0	0
Stock repurchase, Shares	0	0
Stock-based compensation expense related to stock awards granted to employees and consultants	$ 15,423	$ 0	15,423	0	0
Net unrealized gains (losses) on investments - net of taxes	254	0	0	254	0
Net loss	(17,311)	0	0	0	(17,311)
Ending Balance, Amount at Apr. 30, 2019	$ 422,438	$ 15	$ 208,522	$ 351	$ 213,550
Ending Balance, Shares at Apr. 30, 2019	32,738,600	32,738,600