Investments - Additional Information (Detail) $ in Thousands	Jun. 30, 2018 USD ($) AFS_security	Dec. 30, 2017 USD ($)
Investments, Debt Securities [Abstract]
Number of debt securities issues contributing to total unrealized loss \| AFS_security	456
Total, unrealized Losses \| $	$ 76,133	$ 41,863

Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

Name:	us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant