Significant Accounting Policies - Deferred Income Tax Accounts and Tax Reserves (Details) - USD ($)	3 Months Ended	12 Months Ended
Dec. 31, 2017	Dec. 31, 2017	Dec. 25, 2016	Dec. 27, 2015
Significant Accounting Policies
Provisional one-time 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	11,961,000	$ 9,278,000
Decrease (increase) in income tax expense		$ 1,700,000	$ 729,000	$ (731,000)

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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://www.xbrl.org/2003/role/presentationRef
-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