Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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The cumulative amount of the reporting entity's undistributed earnings or deficit.

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Significant accounting policies.

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Summary of Significant Accounting Policies - Additional Information (Detail)	6 Months Ended	12 Months Ended
	Jun. 30, 2016 USD ($) Segment	Dec. 31, 2015 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)
Significant Accounting Policies [Line Items]
Cash and cash equivalents	$ 137,497,000	$ 182,069,000	$ 214,673,000	$ 170,566,000
Accumulated deficit	(239,785,000)	(193,436,000)
Working capital	$ 134,800,000
Number of operating segment \| Segment	1
Cash and cash equivalents maturity period	Three months or less
Impairments of long-lived assets	$ 0	$ 0
Minimum [Member]
Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives	3 years
Maximum [Member]
Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives	5 years
Percentage for the amount of benefit realized upon ultimate settlement	50.00%