Significant Accounting Policies - Deferred Income Tax Accounts and Tax Reserves (Details) - USD ($)	3 Months Ended	12 Months Ended
Dec. 31, 2017	Dec. 30, 2018	Dec. 31, 2017	Dec. 25, 2016
Significant Accounting Policies
Provisional Tax Act tax benefit from remeasurement of deferred tax assets, liabilities and related valuation allowances	$ 7,000,000		$ 7,020,000
Net deferred income tax liability	$ 11,961,000	$ 7,096,000	11,961,000
Decrease in income tax expense		$ 0	$ 1,700,000	$ 729,000

Amount, after deferred tax asset, of deferred tax liability attributable to taxable differences without jurisdictional netting.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=84176650&loc=d3e31931-109318

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319

Name:	us-gaap_DeferredTaxLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant