Long-Term Debt and Long-Term Debt Payable to Related Parties - Carrying Amounts and Estimated Fair Values of Senior Notes (Parenthetical) (Detail)	3 Months Ended
Mar. 31, 2018
2019 Promissory Notes [Member]
Debt Instrument [Line Items]
Maturity date	Dec. 09, 2019
2042 Promissory Notes [Member]
Debt Instrument [Line Items]
Maturity date	Jun. 26, 2042

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_DebtInstrumentMaturityDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration