Fair Value Measurements (Summary of Valuation of Company's Financial Instruments by Various Levels) (Details) - USD ($) $ in Thousands		Sep. 30, 2018	Dec. 31, 2017	Oct. 01, 2017
Assets:
Cash equivalents: money-market funds			$ 12,606
Foreign currency forward contracts	[1]		1,799
Total assets measured at fair value			141,331
Liabilities:
Foreign currency forward contracts	[2]		8,192
Contingent consideration		$ 5,953		$ 0
Total liabilities measured at fair value			8,192
Quoted market prices in active markets (Level 1)
Assets:
Cash equivalents: money-market funds			12,606
Foreign currency forward contracts	[1]		0
Total assets measured at fair value			139,532
Liabilities:
Foreign currency forward contracts	[2]		0
Total liabilities measured at fair value			0
Significant other observable inputs (Level 2)
Assets:
Cash equivalents: money-market funds			0
Foreign currency forward contracts	[1]		1,799
Total assets measured at fair value			1,799
Liabilities:
Foreign currency forward contracts	[2]		8,192
Total liabilities measured at fair value			8,192
Significant unobservable inputs (Level 3)
Assets:
Cash equivalents: money-market funds			0
Foreign currency forward contracts	[1]		0
Total assets measured at fair value			0
Liabilities:
Foreign currency forward contracts	[2]		0
Total liabilities measured at fair value			0
U.S. treasuries
Assets:
Investments, fair value	[3]		124,670
U.S. treasuries | Quoted market prices in active markets (Level 1)
Assets:
Investments, fair value	[3]		124,670
U.S. treasuries | Significant other observable inputs (Level 2)
Assets:
Investments, fair value	[3]		0
U.S. treasuries | Significant unobservable inputs (Level 3)
Assets:
Investments, fair value	[3]		0
Certificates of deposit
Assets:
Investments, fair value	[3]		162
Certificates of deposit | Quoted market prices in active markets (Level 1)
Assets:
Investments, fair value	[3]		162
Certificates of deposit | Significant other observable inputs (Level 2)
Assets:
Investments, fair value	[3]		0
Certificates of deposit | Significant unobservable inputs (Level 3)
Assets:
Investments, fair value	[3]		0
Mutual funds
Assets:
Investments, fair value	[3]		2,094
Mutual funds | Quoted market prices in active markets (Level 1)
Assets:
Investments, fair value	[3]		2,094
Mutual funds | Significant other observable inputs (Level 2)
Assets:
Investments, fair value	[3]		0
Mutual funds | Significant unobservable inputs (Level 3)
Assets:
Investments, fair value	[3]		$ 0
Fair Value, Measurements, Recurring
Assets:
Cash equivalents: money-market funds		37,228
Foreign currency forward contracts	[1]	1,028
Total assets measured at fair value		174,429
Liabilities:
Foreign currency forward contracts	[2]	209
Contingent consideration	[4]	5,953
Total liabilities measured at fair value		6,162
Fair Value, Measurements, Recurring | Quoted market prices in active markets (Level 1)
Assets:
Cash equivalents: money-market funds		37,228
Foreign currency forward contracts	[1]	0
Total assets measured at fair value		173,401
Liabilities:
Foreign currency forward contracts	[2]	0
Contingent consideration	[4]	0
Total liabilities measured at fair value		0
Fair Value, Measurements, Recurring | Significant other observable inputs (Level 2)
Assets:
Cash equivalents: money-market funds		0
Foreign currency forward contracts	[1]	1,028
Total assets measured at fair value		1,028
Liabilities:
Foreign currency forward contracts	[2]	209
Contingent consideration	[4]	0
Total liabilities measured at fair value		209
Fair Value, Measurements, Recurring | Significant unobservable inputs (Level 3)
Assets:
Cash equivalents: money-market funds		0
Foreign currency forward contracts	[1]	0
Total assets measured at fair value		0
Liabilities:
Foreign currency forward contracts	[2]	0
Contingent consideration	[4]	5,953
Total liabilities measured at fair value		5,953
Fair Value, Measurements, Recurring | U.S. treasuries
Assets:
Investments, fair value	[3]	133,164
Fair Value, Measurements, Recurring | U.S. treasuries | Quoted market prices in active markets (Level 1)
Assets:
Investments, fair value	[3]	133,164
Fair Value, Measurements, Recurring | U.S. treasuries | Significant other observable inputs (Level 2)
Assets:
Investments, fair value	[3]	0
Fair Value, Measurements, Recurring | U.S. treasuries | Significant unobservable inputs (Level 3)
Assets:
Investments, fair value	[3]	0
Fair Value, Measurements, Recurring | Certificates of deposit
Assets:
Investments, fair value	[3]	152
Fair Value, Measurements, Recurring | Certificates of deposit | Quoted market prices in active markets (Level 1)
Assets:
Investments, fair value	[3]	152
Fair Value, Measurements, Recurring | Certificates of deposit | Significant other observable inputs (Level 2)
Assets:
Investments, fair value	[3]	0
Fair Value, Measurements, Recurring | Certificates of deposit | Significant unobservable inputs (Level 3)
Assets:
Investments, fair value	[3]	0
Fair Value, Measurements, Recurring | Mutual funds
Assets:
Investments, fair value	[3]	2,857
Fair Value, Measurements, Recurring | Mutual funds | Quoted market prices in active markets (Level 1)
Assets:
Investments, fair value	[3]	2,857
Fair Value, Measurements, Recurring | Mutual funds | Significant other observable inputs (Level 2)
Assets:
Investments, fair value	[3]	0
Fair Value, Measurements, Recurring | Mutual funds | Significant unobservable inputs (Level 3)
Assets:
Investments, fair value	[3]	$ 0

[1] Included in Prepaid expenses and other current assets on the Company’s unaudited condensed consolidated balance sheets.

[2] Included in Other accrued liabilities on the Company’s unaudited condensed consolidated balance sheets.

[3] Included in Short-term investments on the Company’s unaudited condensed consolidated balance sheets.

[4] Included in Other non-current accrued liabilities on the Company’s unaudited condensed consolidated balance sheets. The contingent consideration represents the estimated fair value of the additional variable cash consideration payable in connection with the acquisition of Meural that is contingent upon the achievement of certain technical and service revenue milestones milestones. Refer to Note 5, Business Acquisition, regarding detailed disclosures on the determination of fair value of the contingent consideration.