Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands		12 Months Ended
	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Line Items]
Intangible assets, net		$ 7,660	$ 9,688
Goodwill		$ 42,748	$ 42,648
Expected dividend yield		0.00%
Percentage of tax benefit realized upon ultimate settlement with taxing authority		50.00%
Long-Lived Assets of Several Centers
Accounting Policies [Line Items]
Intangible assets, net		$ 13,900
Customer Concentration Risk | Accounts Receivable
Accounting Policies [Line Items]
Percentage of accounts receivable		10.00%
Major Customer One | Customer Concentration Risk | Accounts Receivable
Accounting Policies [Line Items]
Percentage of accounts receivable			12.00%
Major Customer Two | Customer Concentration Risk | Accounts Receivable
Accounting Policies [Line Items]
Percentage of accounts receivable			10.00%
System One
Accounting Policies [Line Items]
Goodwill		$ 41,100
In-Center
Accounting Policies [Line Items]
Goodwill		500
Services
Accounting Policies [Line Items]
Asset impairment recognized		300	$ 500	$ 200
Goodwill		1,100
Federal
Accounting Policies [Line Items]
Net operating loss carryforward		390,000
State
Accounting Policies [Line Items]
Net operating loss carryforward		$ 182,000
Accounting Standards Update 2014-09 | Scenario, Forecast | Services
Accounting Policies [Line Items]
Goodwill, impairment loss	$ 1,100
Accounting Standards Update 2016-09 | Federal
Accounting Policies [Line Items]
Net operating loss carryforward	18,000
Accounting Standards Update 2016-09 | State
Accounting Policies [Line Items]
Net operating loss carryforward	$ 1,600