Debt instrument conversion obligation number of consecutive business days after consecutive trading day period.

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Debt instrument conversion obligation period of consecutive trading days.

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Debt instrument conversion obligation trading price as percentage of product common stock closing sale price and conversion rate.

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Debt instrument convertible initial conversion price per share of common stock.

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- Definition

Debt instrument effective interest rate period.

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Debt instrument percentage of cash or cash equivalents addition to principal balance.

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- Definition

Debt issuance costs allocated to equity component in reduction to additional paid in capital.

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Debt issuance costs allocated to liability component.

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Number of equity instruments issuable after debt instrument convertible.

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- Definition

Amount of increase (decrease) in additional paid in capital (APIC) resulting from recognition of deferred taxes for convertible debt with a beneficial conversion feature.

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Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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The price per share of the conversion feature embedded in the debt instrument.

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Threshold period of specified consecutive trading days within which common stock price to conversion price of convertible debt instrument must exceed threshold percentage for specified number of trading days to trigger conversion feature.

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Minimum percentage of common stock price to conversion price of convertible debt instruments to determine eligibility of conversion.

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Threshold number of specified trading days that common stock price to conversion price of convertible debt instruments must exceed threshold percentage within a specified consecutive trading period to trigger conversion feature.

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Date the debt agreement requires the first payment to be made, in CCYY-MM-DD format.

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Identification of the lender and information about a contractual promise to repay a short-term or long-term obligation, which includes borrowings under lines of credit, notes payable, commercial paper, bonds payable, debentures, and other contractual obligations for payment. This may include rationale for entering into the arrangement, significant terms of the arrangement, which may include amount, repayment terms, priority, collateral required, debt covenants, borrowing capacity, call features, participation rights, conversion provisions, sinking-fund requirements, voting rights, basis for conversion if convertible and remarketing provisions. The description may be provided for individual debt instruments, rational groupings of debt instruments, or by debt in total.

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Face (par) amount of debt instrument at time of issuance.

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Description of the frequency of periodic payments (monthly, quarterly, annual).

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Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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Description of the payment terms of the debt instrument (for example, whether periodic payments include principal and frequency of payments) and discussion about any contingencies associated with the payment.

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Start date of debt instrument redemption period, in CCYY-MM-DD format.

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Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of the cost of borrowed funds accounted for as interest expense for debt.

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Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The cash outflow paid to third parties in connection with debt origination, which will be amortized over the remaining maturity period of the associated long-term debt.

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The cash inflow from the issuance of a long-term debt instrument which can be exchanged for a specified amount of another security, typically the entity's common stock, at the option of the issuer or the holder.

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Amount of cash inflow from contractual arrangement with the lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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Debt - Additional Information (Detail)				3 Months Ended		12 Months Ended
Debt - Additional Information (Detail)	May 02, 2017 USD ($)	Jul. 22, 2016 USD ($)	Aug. 04, 2015 USD ($)	Mar. 31, 2018 USD ($) d $ / shares shares	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Term loan due within 12 months				$ 9,967,000		$ 9,967,000
Term loan due in greater than 12 months				10,612,000		12,936,000
Equity component of Convertible Notes recorded as additional paid-in capital						$ 62,466,000
Amortization of debt discount				(230,000)	$ 155,000
2015 Term Loan [Member]
Debt Instrument [Line Items]
Carrying value of term loan				20,579,000
Liability component of Convertible Notes recorded as long-term debt				$ 23,088,000
Mid Cap Financial Trust [Member] \| 2015 Term Loan [Member]
Debt Instrument [Line Items]
Term loan, maximum borrowings			$ 30,000,000
Debt instrument description				The Company also agreed to maintain a balance in cash or cash equivalents at Silicon Valley Bank equal to the principal balance of the loan plus 5%.
Debt instrument percentage of cash or cash equivalents addition to principal balance			5.00%
Debt instrument interest rate			6.25%
Term loan, first periodic payment date			Mar. 01, 2017
Debt instrument maturity date			Feb. 01, 2020
Interest on final payment			9.00%
Term loan, payment description				Interest-only period of 19 months, principal will be due in 36 equal monthly installments.
Carrying value of term loan				$ 20,600,000
Term loan due within 12 months				10,000,000
Term loan due in greater than 12 months				$ 10,600,000
Debt issuance costs			$ 150,000
Mid Cap Financial Trust [Member] \| 2015 Term Loan [Member] \| Interest-Only-Strip [Member]
Debt Instrument [Line Items]
Term loan, Interest payment period			19 months
Mid Cap Financial Trust [Member] \| 2015 Term Loan [Member] \| Principal-Only-Strip [Member]
Debt Instrument [Line Items]
Term loan, Interest payment period			36 months
Mid Cap Financial Trust [Member] \| 2015 Term Loan [Member] \| Initial Term Loan [Member]
Debt Instrument [Line Items]
Term loan, currently borrowed			$ 15,000,000
Mid Cap Financial Trust [Member] \| 2015 Term Loan [Member] \| Second Term Loan [Member]
Debt Instrument [Line Items]
Term loan remaining amount borrowed		$ 15,000,000
2024 Convertible Notes [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	3.375%			3.375%
Debt instrument maturity date	May 01, 2024
Interest on final payment	3.375%			9.71%
Debt issuance costs	$ 6,500,000			$ 68,900,000
Debt instrument principal amount	201,300,000
Debt instrument frequency of periodic payment				semi-annually
Net proceeds from offering of convertible senior notes	194,800,000
Debt conversion, converted instrument, shares issued \| shares				37.3413
Debt instrument principal amount denomination for conversion in to common stock \| $ / shares				$ 1,000
Debt instrument convertible initial conversion price per share of common stock \| $ / shares				$ 26.78
Number of days within 30 consecutive trading days in which the closing price of the entity's common stock must exceed the conversion price for the notes to be convertible into common stock \| d				20
Number of consecutive trading days during which the closing price of the entity's common stock must exceed the conversion price for at least 20 days in order for the notes to be convertible into common stock \| d				30
Percentage of the closing sales price of the entity's common stock that the conversion price must exceed in order for the notes to be convertible				130.00%
Number of consecutive business days immediately after any five consecutive trading day period during the note measurement period \| d				5
Number of consecutive trading days before five consecutive business days during the note measurement period \| d				10
Liability component of Convertible Notes recorded as long-term debt	136,700,000
Equity component of Convertible Notes recorded as additional paid-in capital	$ 64,500,000
Debt instrument effective interest rate period				7 years
Debt issuance costs				$ 6,500,000
Debt issuance costs allocated to liability component				4,400,000
Debt issuance costs allocated to equity component reduction to additional paid-in capital				2,100,000
Interest expense				3,400,000
Amortization of debt discount				$ 1,700,000
2024 Convertible Notes [Member] \| On or After February 1, 2024 [Member]
Debt Instrument [Line Items]
Number of days within 30 consecutive trading days in which the closing price of the entity's common stock must exceed the conversion price for the notes to be convertible into common stock \| d				20
Number of consecutive trading days during which the closing price of the entity's common stock must exceed the conversion price for at least 20 days in order for the notes to be convertible into common stock \| d				30
Percentage of the closing sales price of the entity's common stock that the conversion price must exceed in order for the notes to be convertible				130.00%
Debt instrument redemption date				May 06, 2020
Redemption price percentage of principal amount to be redeemed				100.00%
2024 Convertible Notes [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Debt instrument conversion obligation trading price as percentage of product common stock closing sale price and conversion rate				98.00%