Significant Accounting Policies - Concentration of Risks (Details) $ in Thousands	12 Months Ended
Dec. 31, 2016 USD ($) customer Agency	Dec. 31, 2015 USD ($) Agency	Dec. 31, 2014 Agency
Concentration of risks
Cash, cash equivalents and short-term investments	$ 395,954	$ 335,879
Current liabilities denominated in RMB	278,103	208,775
Cash, cash equivalents and short-term investments \| Concentration of credit risk \| China
Concentration of risks
Cash, cash equivalents and short-term investments	$ 393,600	334,600
Maximum term of original maturity of time deposits	12 months
Cash, cash equivalents and short-term investments \| Concentration of foreign currency risks \| RMB
Concentration of risks
Cash, cash equivalents and short-term investments	$ 335,700	$ 157,900
Percentage of benchmark derived from specified source	85.00%	47.00%
Consolidated net revenues benchmark \| Customer concentration risk \| Alibaba
Concentration of risks
Percentage of benchmark derived from specified source	9.00%	30.00%	32.00%
Consolidated net accounts receivables benchmark \| Concentration of credit risk \| Alibaba
Concentration of risks
Percentage of benchmark derived from specified source	21.00%	45.00%
Consolidated net accounts receivables benchmark \| Concentration of credit risk \| Customer
Concentration of risks
Percentage of benchmark derived from specified source	15.00%	16.00%
Number of customers \| customer	1
Consolidated net accounts receivables benchmark \| Concentration of foreign currency risks \| RMB
Concentration of risks
Accounts receivable denominated in RMB	$ 115,300	$ 120,100
Current liabilities \| Concentration of foreign currency risks \| RMB
Concentration of risks
Current liabilities denominated in RMB	$ 267,800	$ 197,900
Percentage of benchmark derived from specified source	96.00%	95.00%
Advertising & Marketing \| Consolidated net revenues benchmark \| Customer concentration risk \| Top 10 advertising agencies \| China
Concentration of risks
Number of advertising agencies \| Agency	10	10	10
Percentage of benchmark derived from specified source	22.00%	15.00%	14.00%

Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Total obligations incurred as part of normal operations that are expected to be paid during the following twelve months or within one business cycle, if longer.

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