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Shareholders' Equity (Detail) - USD ($)	1 Months Ended		3 Months Ended	6 Months Ended
	Jan. 31, 2016	Feb. 28, 2015	Jun. 30, 2016	Jun. 30, 2016	Jun. 30, 2015	May 31, 2016	May 18, 2016
Class of Stock [Line Items]
Stock issued during period		3,400,000
Share price (in USD per share)		$ 20.03
Proceeds from issuance of common stock and pre-funded warrants, net		$ 79,100,000		$ 724,000	$ 79,076,000
Shares of common stock to purchase by warrant (in shares)		749,250
Warrant exercise price (in USD per share)		$ 0.01
Offering expenses and underwriter discounts		$ 4,900,000
Proceeds from warrant exercises				$ 1,900,000
Warrants exercised during period				1,171,775
Pre-funded Warrants
Class of Stock [Line Items]
Share price (in USD per share)		$ 20.02
At The Market (ATM) Program
Class of Stock [Line Items]
Aggregate offering price for ATM program	$ 100,000,000
Stock offering ATM program, commission percent	1.70%
Stock offering ATM program, notice period for termination	10 days
Stock issued during period			64,565
Proceeds from issuance of common stock and pre-funded warrants, net			$ 724,000
At The Market (ATM) Program | Weighted Average
Class of Stock [Line Items]
Share price (in USD per share)			$ 11.41	$ 11.41
Oxford EWB Loan
Class of Stock [Line Items]
Shares of common stock to purchase by warrant (in shares)						100,602	100,602
Warrant exercise price (in USD per share)						$ 9.94	$ 9.94
Oxford EWB Loan | Long-term Debt
Class of Stock [Line Items]
Warrant fair value							$ 758,000

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