Consolidated Statements of Shareholders' Equity - 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, 2016	$ 349,456	$ 15	$ 176,306	$ (7)	$ 173,142
Beginning Balance, Shares at Jan. 31, 2016		32,333,359
Cumulative effect of change in accounting principle	11,688	$ 0	227	0	11,461
Exercise of stock options, Amount	$ 3,230	$ 0	3,230	0	0
Exercise of stock options, Shares	235,923	235,923
Restricted stock awards granted, Amount	$ 0	$ 0	0	0	0
Restricted stock awards granted, Shares		184,155
Vesting of restricted stock units, Amount	0	$ 0	0	0	0
Vesting of restricted stock units, Shares		894,710
Employee stock purchase plan, Amount	4,034	$ 0	4,034	0	0
Employee stock purchase plan, Shares		125,974
Stock repurchase, Amount	(20,183)	$ 0	(20,183)	0	0
Stock repurchase, Shares		(405,089)
Stock-based compensation expense related to stock awards granted to employees and consultants	48,832	$ 0	48,832	0	0
Excess income tax benefit associated with stock-based compensation	(170)	0	(170)	0	0
Net unrealized gains (losses) on investments - net of taxes	(63)	0	0	(63)	0
Net income (loss)	57,810	0	0	0	57,810
Ending Balance, Amount at Jan. 31, 2017	454,634	$ 15	212,276	(70)	242,413
Ending Balance, Shares at Jan. 31, 2017		33,369,032
Exercise of stock options, Amount	$ 2,191	$ 0	2,191	0	0
Exercise of stock options, Shares	175,187	175,187
Vesting of restricted stock units, Amount	$ 0	$ 0	0	0	0
Vesting of restricted stock units, Shares		932,454
Employee stock purchase plan, Amount	4,646	$ 0	4,646	0	0
Employee stock purchase plan, Shares		107,736
Stock repurchase, Amount	(54,788)	$ 0	(54,788)	0	0
Stock repurchase, Shares		(1,094,795)
Stock-based compensation expense related to stock awards granted to employees and consultants	56,861	$ 0	56,861	0	0
Net unrealized gains (losses) on investments - net of taxes	(209)	0	0	(209)	0
Net income (loss)	18,852	0	0	0	18,852
Ending Balance, Amount at Jan. 31, 2018	$ 482,187	$ 15	221,186	(279)	261,265
Ending Balance, Shares at Jan. 31, 2018	33,489,614	33,489,614
Cumulative effect of change in accounting principle	$ 43	$ 0	0	0	43
Exercise of stock options, Amount	$ 1,285	$ 0	1,285	0	0
Exercise of stock options, Shares	232,205	232,205
Vesting of restricted stock units, Amount	$ 0	$ 0	0	0	0
Vesting of restricted stock units, Shares		920,826
Employee stock purchase plan, Amount	5,136	$ 0	5,136	0	0
Employee stock purchase plan, Shares		146,887
Stock repurchase, Amount	$ (99,903)	$ 0	(99,903)	0	0
Stock repurchase, Shares	(2,485,992)	(2,485,992)
Stock-based compensation expense related to stock awards granted to employees and consultants	$ 60,812	$ 0	60,812	0	0
Net unrealized gains (losses) on investments - net of taxes	376	0	0	376	0
Net income (loss)	(30,447)	0	0	0	(30,447)
Ending Balance, Amount at Jan. 31, 2019	$ 419,489	$ 15	$ 188,516	$ 97	$ 230,861
Ending Balance, Shares at Jan. 31, 2019	32,303,540	32,303,540