Shareholders' Equity - Additional Information (Detail) - USD ($)		1 Months Ended	3 Months Ended	9 Months Ended	14 Months Ended
	Sep. 30, 2015	Aug. 31, 2014	Sep. 30, 2015	Sep. 30, 2015	Sep. 30, 2015
Equity Distribution Agreement [Member]
Shareholders Equity [Line Items]
Net sales commissions			$ 299,000	$ 299,000	$ 700,000
Stock issuance cost			$ 82,000	$ 82,000	$ 415,000
Shares sold under equity distribution agreement	0
Common Stock [Member]
Shareholders Equity [Line Items]
Issuance of common stock				342,000
Common Stock [Member] | Equity Distribution Agreement [Member]
Shareholders Equity [Line Items]
Issuance of common stock			342,000	342,000	1,026,000
Weighted average price per share			$ 38.83	$ 38.83	$ 29.24
Cash proceeds from shares sold			$ 12,978,000	$ 12,978,000	$ 29,300,000
Maximum [Member]
Shareholders Equity [Line Items]
Aggregate offering price for common stock		$ 30,000,000