Commitments and Contingencies - Additional Information (Detail) - USD ($)	6 Months Ended	12 Months Ended
Jun. 30, 2015	Dec. 31, 2014
Loss Contingencies [Line Items]
Commitments for capital expenditure	$ 28,000,000	$ 31,800,000
Accrual related to litigation	$ 0	$ 350,000

Future cash outflow to pay for purchases of fixed assets that have occurred.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4332-108586

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4313-108586

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration