Significant Accounting Policies and Practices (Details)	1 Months Ended		3 Months Ended										11 Months Ended	12 Months Ended
	May 31, 2017 USD ($)	Oct. 31, 2014 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) voting_interest_model_entity variable_interest_entity partnership	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jan. 03, 2018	Oct. 31, 2012 USD ($)
Significant Accounting Policies [Line Items]
Cash and cash equivalents restricted to withdrawals				$ 300,000				$ 300,000					$ 300,000	$ 300,000	$ 300,000
Allowance for doubtful accounts				700,000				400,000					700,000	700,000	400,000
Impairment loss as a result of goodwill														$ 0	0	$ 0
Forecasted period for income statement and working capital projections to assess goodwill impairment														5 years
Debt issuance costs				1,000,000				1,600,000					1,000,000	$ 1,000,000	1,600,000
Accumulated amortization of debt issuance costs				9,700,000				9,000,000					9,700,000	9,700,000	9,000,000
Amortization expense														700,000	800,000	900,000
Book overdrafts				29,000,000				36,500,000					29,000,000	29,000,000	36,500,000
Reimbursed management contract revenue				166,500,000	$ 165,100,000	$ 168,600,000	$ 179,000,000	174,800,000	$ 177,000,000	$ 168,100,000	$ 156,700,000			679,200,000	676,600,000	650,600,000
Reimbursed management contract expense				166,500,000	165,100,000	168,600,000	179,000,000	174,800,000	177,000,000	168,100,000	156,700,000			679,200,000	676,600,000	650,600,000
Advertising expenses														1,500,000	1,200,000	1,600,000
Gain on sale of equity method Investee														8,500,000
Equity earnings in related investments														11,300,000	2,400,000	2,000,000
Ownership percentage		30.00%
Recognition of pre-tax gain		$ 4,100,000
Cash received from sale of business, net														600,000	0	1,000,000
Excess tax benefit														900,000
Reclassification into deferred tax asset, non current				15,900,000				17,900,000					$ 15,900,000	15,900,000	17,900,000
Lease contracts	$ 124,400,000			131,400,000	131,000,000	130,200,000	125,800,000	125,200,000	125,800,000	124,000,000	130,600,000			518,400,000	505,600,000	532,800,000
Depreciation and amortization				$ 4,700,000	$ 4,900,000	$ 4,800,000	$ 6,600,000	6,900,000	$ 7,800,000	$ 9,800,000	9,200,000			21,000,000	33,700,000	34,000,000
Discontinued Operations, Disposed of by Sale | Security Business
Significant Accounting Policies [Line Items]
Sale price of business												$ 1,800,000
Gain on sale of business								500,000
Cash received from sale of business, net								$ 1,000,000
Period of cash consideration to be received								18 months				18 months
Period to calculate and remit remaining consideration													60 days
Contingent consideration receivable from sale of business								$ 600,000				$ 500,000
Additional earn out consideration														$ 100,000
Minimum
Significant Accounting Policies [Line Items]
Voting interest ownership percentage				30.00%									30.00%	30.00%
Maximum
Significant Accounting Policies [Line Items]
Voting interest ownership percentage				50.00%									50.00%	50.00%
Equipment | Minimum
Significant Accounting Policies [Line Items]
Ranges of estimated useful life														1 year
Equipment | Maximum
Significant Accounting Policies [Line Items]
Ranges of estimated useful life														10 years
Leasehold improvements | Maximum
Significant Accounting Policies [Line Items]
Ranges of estimated useful life														10 years
Leasehold improvements | Average
Significant Accounting Policies [Line Items]
Ranges of estimated useful life														8 years 6 months
Partnerships and joint ventures
Significant Accounting Policies [Line Items]
Number of ownership interest entities | partnership														31
Interest rate swaps | Cash flow hedges
Significant Accounting Policies [Line Items]
Aggregate starting notional amount																		$ 150,000,000.0
Fixed rate (as a percentage)																		0.7525%
Variable rate basis														LIBOR
Ineffective portion of cash flow hedges recognized														$ 0
Central Merger
Significant Accounting Policies [Line Items]
Cost of property repairs and maintenance														$ 100,000	700,000	4,600,000
Variable Interest Entity, Primary Beneficiary
Significant Accounting Policies [Line Items]
Number of ownership interest entities | variable_interest_entity														24
Variable Interest Entity, Not Primary Beneficiary
Significant Accounting Policies [Line Items]
Number of ownership interest entities | voting_interest_model_entity														7
Accounting Standards Update 2016-09, Forfeiture Rate Component | New Accounting Pronouncement, Early Adoption, Effect
Significant Accounting Policies [Line Items]
Stock-based compensation expense															300,000
Accounting Standards Update 2015-07 | New Accounting Pronouncement, Early Adoption, Effect
Significant Accounting Policies [Line Items]
Reclassification into deferred tax asset, non current																12,300,000
Additional Paid-in Capital | Accounting Standards Update 2016-09, Forfeiture Rate Component | New Accounting Pronouncement, Early Adoption, Effect
Significant Accounting Policies [Line Items]
Cumulative effect adjustment upon adoption of new accounting standard on January 1, 2017											$ 300,000
Reimbursed Management Contract Revenue and Expense
Significant Accounting Policies [Line Items]
Reimbursed management contract revenue															47,100,000	44,100,000
Reimbursed management contract expense															$ 47,100,000	$ 44,100,000
Subsequent Event
Significant Accounting Policies [Line Items]
Voting interest ownership percentage																	30.00%
Subsequent Event | Discontinued Operations, Disposed of by Sale | Parkmobile
Significant Accounting Policies [Line Items]
Voting interest ownership percentage																	30.00%
Forecast | Discontinued Operations, Disposed of by Sale | Parkmobile
Significant Accounting Policies [Line Items]
Sale price of business			$ 19,000,000
Gain on sale of business			$ 10,100,000
Lease Contracts
Significant Accounting Policies [Line Items]
Depreciation and amortization	200,000
Management Contracts
Significant Accounting Policies [Line Items]
Depreciation and amortization	$ 100,000