Condensed Balance Sheets (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Current assets
Cash and cash equivalents	$ 282,081,829	$ 196,113,315	$ 119,561,152	$ 136,859,336
Deferred tax assets	3,522,054us-gaap_DeferredTaxAssetsNetCurrent	784,063us-gaap_DeferredTaxAssetsNetCurrent
Other current assets	9,430,135us-gaap_OtherAssetsCurrent	4,695,947us-gaap_OtherAssetsCurrent
Total current assets	366,365,993us-gaap_AssetsCurrent	262,706,996us-gaap_AssetsCurrent
Investment in subsidiaries and VIEs	35,817,261	14,742,364
Non-current deferred tax assets	2,262,489us-gaap_DeferredTaxAssetsNetNoncurrent	1,494,769us-gaap_DeferredTaxAssetsNetNoncurrent
Other non-current assets	1,930,814us-gaap_OtherAssetsNoncurrent	1,220,033us-gaap_OtherAssetsNoncurrent
Total assets	431,100,062us-gaap_Assets	303,254,657us-gaap_Assets
Current liabilities
Other current liabilities	27,259,639us-gaap_OtherLiabilitiesCurrent	15,227,247us-gaap_OtherLiabilitiesCurrent
Total current liabilities	111,651,738us-gaap_LiabilitiesCurrent	62,813,010us-gaap_LiabilitiesCurrent
Uncertain tax position liabilities	1,793,459	1,650,399
Other non-current liabilities	5,004,281us-gaap_OtherLiabilitiesNoncurrent	3,596,295us-gaap_OtherLiabilitiesNoncurrent
Total liabilities	118,449,478us-gaap_Liabilities	68,059,704us-gaap_Liabilities
Shareholders' equity
Ordinary shares ($0.0005 par value): 94,100,000 shares authorized, 28,715,882 shares issued and 27,648,066 shares outstanding as of December 31, 2013 and 29,123,118 shares issued and 28,055,302 shares outstanding as of December 31, 2014	14,561us-gaap_CommonStockValue	14,358us-gaap_CommonStockValue
Treasury stock (1,067,816 ordinary shares at both December 31, 2013 and December 31, 2014)	(11,675,955)us-gaap_TreasuryStockValue	(11,675,955)us-gaap_TreasuryStockValue
Additional paid-in capital	135,640,392	129,687,092
Retained earnings	169,525,124	97,118,620
Accumulated other comprehensive income	5,118,141	9,281,049
Total shareholders' equity	298,622,263us-gaap_StockholdersEquity	224,425,164us-gaap_StockholdersEquity
Total Liabilities and Equity	431,100,062	303,254,657
Parent Company
Current assets
Cash and cash equivalents	28,871,793	42,689,231	50,987,910	84,371,832
Due from subsidiaries and VIEs	36,220,656	38,453,506
Deferred tax assets	78,574	64,755
Other current assets	4,143,658	730,102
Total current assets	69,314,681	81,937,594
Investment in subsidiaries and VIEs	232,083,557	144,678,555
Non-current deferred tax assets	430,578	389,615
Other non-current assets	50,000
Total assets	301,878,816	227,005,764
Current liabilities
Other current liabilities	1,185,921	691,734
Total current liabilities	1,185,921	691,734
Uncertain tax position liabilities	774,284	605,820
Other non-current liabilities	1,296,348	1,283,046
Total liabilities	3,256,553	2,580,600
Shareholders' equity
Ordinary shares ($0.0005 par value): 94,100,000 shares authorized, 28,715,882 shares issued and 27,648,066 shares outstanding as of December 31, 2013 and 29,123,118 shares issued and 28,055,302 shares outstanding as of December 31, 2014	14,561	14,358
Treasury stock (1,067,816 ordinary shares at both December 31, 2013 and December 31, 2014)	(11,675,955)	(11,675,955)
Additional paid-in capital	135,640,392	129,687,092
Retained earnings	169,525,124	97,118,620
Accumulated other comprehensive income	5,118,141	9,281,049
Total shareholders' equity	298,622,263	224,425,164
Total Liabilities and Equity	$ 301,878,816	$ 227,005,764

Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 11

-URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e637-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 14

-URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e681-108580

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 14A

-URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669686-108580

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 31

-Article 5

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3