Long-Term Debt - Schedule of Revolving Credit Facility and Long-Term Debt (Parenthetical) (Detail)	Mar. 31, 2019	Dec. 31, 2017
6.0% Working Capital Revolver Loan [Member]
Debt Instrument [Line Items]
Line of credit facility, interest rate	6.00%	6.00%
5.73% Secured Promissory Note Due 2019 [Member]
Debt Instrument [Line Items]
Long-term debt, effective Interest Rate	5.73%	5.73%
5.25% Secured Promissory Note Due 2021 [Member]
Debt Instrument [Line Items]
Long-term debt, effective Interest Rate	5.25%	5.25%
6.74% Secured Promissory Note Due 2023 [Member]
Debt Instrument [Line Items]
Long-term debt, effective Interest Rate	6.74%	6.74%

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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6036836-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant