Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Summary Of Significant Accounting Policies [Line Items]
Cash equivalents maturity, description	Cash equivalents consist of short-term, highly liquid investments with original maturities of three months or less from the date of purchase.
Impact on revenue, change in accounting estimate	$ 7,216,000	$ 5,924,000
Impact on loss per share, change in accounting estimate	$ (0.19)	$ (1.29)
Debt discount and issuance liability component, current	188,000		76,000
Debt discount and issuance liability component, non-current	245,000		11,000
Change in Accounting Method Accounted for as Change in Estimate [Member]
Summary Of Significant Accounting Policies [Line Items]
Impact on revenue, change in accounting estimate	$ 100,000
Impact of change in accounting estimate	The Company changed its revenue recognized from two of its payers from a cash basis to an accrual basis based on the Company's consistent history of obtaining reimbursement from these two payers. The impact of this change in accounting estimate is to increase revenues by $100,000 and to change loss per share from $0.20 to $0.19 for the three months ended March 31, 2015.
Change in Accounting Method Accounted for as Change in Estimate [Member] | Previously Reported [Member]
Summary Of Significant Accounting Policies [Line Items]
Impact on loss per share, change in accounting estimate	$ (0.20)