CONDENSED CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Ordinary Shares	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings
Beginning balance (in shares) at Dec. 31, 2017		51,487,650
Beginning balance at Dec. 31, 2017	$ 1,057,448	$ 221	$ 873,979	$ 1,618	$ 181,630
Increase (Decrease) in Stockholders' Equity
Net income	37,843				37,843
Unrealized gains (losses) on available-for-sale securities and derivative contracts, net of taxes	(1,631)			(1,631)
Share-based compensation	14,974		14,974
Issuances of shares through employee equity incentive plans (in shares)		384,523
Issuances of shares through employee equity incentive plans	2,710	$ 2	2,708
Issuance of shares through employee share purchase plan (in shares)		288,017
Issuance of shares through employee share purchase plan	11,348	$ 1	11,347
Ending balance (in shares) at Mar. 31, 2018		52,160,190
Ending balance at Mar. 31, 2018	1,127,193	$ 224	903,008	(13)	223,974
Beginning balance (in shares) at Dec. 31, 2017		51,487,650
Beginning balance at Dec. 31, 2017	1,057,448	$ 221	873,979	1,618	181,630
Increase (Decrease) in Stockholders' Equity
Net income	91,426
Unrealized gains (losses) on available-for-sale securities and derivative contracts, net of taxes	(1,785)			(1,785)
Ending balance (in shares) at Sep. 30, 2018		53,517,077
Ending balance at Sep. 30, 2018	1,233,903	$ 232	956,281	(167)	277,557
Beginning balance (in shares) at Mar. 31, 2018		52,160,190
Beginning balance at Mar. 31, 2018	1,127,193	$ 224	903,008	(13)	223,974
Increase (Decrease) in Stockholders' Equity
Net income	16,526				16,526
Unrealized gains (losses) on available-for-sale securities and derivative contracts, net of taxes	(2,169)			(2,169)
Share-based compensation	14,916		14,916
Issuances of shares through employee equity incentive plans (in shares)		770,573
Issuances of shares through employee equity incentive plans	5,283	$ 5	5,278
Ending balance (in shares) at Jun. 30, 2018		52,930,763
Ending balance at Jun. 30, 2018	1,161,749	$ 229	923,202	(2,182)	240,500
Increase (Decrease) in Stockholders' Equity
Net income	37,057				37,057
Unrealized gains (losses) on available-for-sale securities and derivative contracts, net of taxes	2,015			2,015
Share-based compensation	19,156		19,156
Issuances of shares through employee equity incentive plans (in shares)		384,208
Issuances of shares through employee equity incentive plans	2,424	$ 2	2,422
Issuance of shares through employee share purchase plan (in shares)		202,106
Issuance of shares through employee share purchase plan	11,502	$ 1	11,501
Ending balance (in shares) at Sep. 30, 2018		53,517,077
Ending balance at Sep. 30, 2018	1,233,903	$ 232	956,281	(167)	277,557
Beginning balance (in shares) at Dec. 31, 2018		53,918,208
Beginning balance at Dec. 31, 2018	1,301,648	$ 233	982,677	(1,051)	319,789
Increase (Decrease) in Stockholders' Equity
Net income	48,620				48,620
Unrealized gains (losses) on available-for-sale securities and derivative contracts, net of taxes	3,373			3,373
Share-based compensation	24,242		24,242
Issuances of shares through employee equity incentive plans (in shares)		451,535
Issuances of shares through employee equity incentive plans	5,972	$ 2	5,970
Issuance of shares through employee share purchase plan (in shares)		162,573
Issuance of shares through employee share purchase plan	11,055	$ 1	11,054
Ending balance (in shares) at Mar. 31, 2019		54,532,316
Ending balance at Mar. 31, 2019	1,394,910	$ 236	1,023,943	2,322	368,409
Beginning balance (in shares) at Dec. 31, 2018		53,918,208
Beginning balance at Dec. 31, 2018	1,301,648	$ 233	982,677	(1,051)	319,789
Increase (Decrease) in Stockholders' Equity
Net income	131,228
Unrealized gains (losses) on available-for-sale securities and derivative contracts, net of taxes	5,318			4,015
Issuance of shares through employee share purchase plan (in shares)		147,150
Issuance of shares through employee share purchase plan	13,389	$ 1	13,388
Ending balance (in shares) at Sep. 30, 2019		55,457,941
Ending balance at Sep. 30, 2019	1,552,268	$ 240	1,096,744	2,964	452,320
Beginning balance (in shares) at Mar. 31, 2019		54,532,316
Beginning balance at Mar. 31, 2019	1,394,910	$ 236	1,023,943	2,322	368,409
Increase (Decrease) in Stockholders' Equity
Net income	38,429				38,429
Unrealized gains (losses) on available-for-sale securities and derivative contracts, net of taxes	1,375			72	1,303
Share-based compensation	26,949		26,949
Issuances of shares through employee equity incentive plans (in shares)		262,557
Issuances of shares through employee equity incentive plans	1,094	$ 1	1,093
Ending balance (in shares) at Jun. 30, 2019		54,794,873
Ending balance at Jun. 30, 2019	1,462,757	$ 237	1,051,985	2,394	408,141
Increase (Decrease) in Stockholders' Equity
Net income	44,179				44,179
Unrealized gains (losses) on available-for-sale securities and derivative contracts, net of taxes	570			570
Share-based compensation	31,226		31,226
Issuances of shares through employee equity incentive plans (in shares)		515,918
Issuances of shares through employee equity incentive plans	147	$ 2	145
Ending balance (in shares) at Sep. 30, 2019		55,457,941
Ending balance at Sep. 30, 2019	$ 1,552,268	$ 240	$ 1,096,744	$ 2,964	$ 452,320