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
Issuance of shares through employee equity incentive plan, Amount	305	$ 0	305	0	0
Issuance of shares through employee equity incentive plan, Shares		272,723
Issuance of shares through employee stock purchase plan, Amount	2,818	$ 0	2,818	0	0
Issuance of shares through 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, 2018	482,187	$ 15	221,186	(279)	261,265
Beginning Balance, Shares at Jan. 31, 2018		33,489,614
Net unrealized gains (losses) on investments - net of taxes	68
Net loss	(16,883)
Ending Balance, Amount at Jul. 31, 2018	432,892	$ 15	188,663	(211)	244,425
Ending Balance, Shares at Jul. 31, 2018		32,650,237
Beginning Balance, Amount at Apr. 30, 2018	468,808	$ 15	217,880	(389)	251,302
Beginning Balance, Shares at Apr. 30, 2018		33,396,304
Issuance of shares through employee equity incentive plan, Amount	642	$ 0	642	0	0
Issuance of shares through employee equity incentive plan, Shares		373,126
Stock repurchase, Amount	(44,989)	$ 0	(44,989)	0	0
Stock repurchase, Shares		(1,119,193)
Stock-based compensation expense related to stock awards granted to employees and consultants	15,130	$ 0	15,130	0	0
Net unrealized gains (losses) on investments - net of taxes	178	0	0	178	0
Net loss	(6,877)	0	0	0	(6,877)
Ending Balance, Amount at Jul. 31, 2018	432,892	$ 15	188,663	(211)	244,425
Ending Balance, Shares at Jul. 31, 2018		32,650,237
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
Issuance of shares through employee equity incentive plan, Amount	$ 1,520	$ 0	1,520	0	0
Issuance of shares through employee equity incentive plan, Shares		335,301
Issuance of shares through employee stock purchase plan, Amount	3,063	$ 0	3,063	0	0
Issuance of shares through employee stock purchase plan, Shares		99,759
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
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
Stock repurchase, Shares	0
Net unrealized gains (losses) on investments - net of taxes	$ 448
Net loss	(27,502)
Ending Balance, Amount at Jul. 31, 2019	$ 428,461	$ 15	224,542	545	203,359
Ending Balance, Shares at Jul. 31, 2019	33,033,619	33,033,619
Beginning Balance, Amount at Apr. 30, 2019	$ 422,438	$ 15	208,522	351	213,550
Beginning Balance, Shares at Apr. 30, 2019		32,738,600
Issuance of shares through employee equity incentive plan, Amount	$ 988	$ 0	988	0	0
Issuance of shares through employee equity incentive plan, Shares		295,019
Stock repurchase, Shares	0
Stock-based compensation expense related to stock awards granted to employees and consultants	$ 15,032	$ 0	15,032	0	0
Net unrealized gains (losses) on investments - net of taxes	194	0	0	194	0
Net loss	(10,191)	0	0	0	(10,191)
Ending Balance, Amount at Jul. 31, 2019	$ 428,461	$ 15	$ 224,542	$ 545	$ 203,359
Ending Balance, Shares at Jul. 31, 2019	33,033,619	33,033,619