Description of Business and Significant Accounting Policies (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($) financial_institution	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) segment financial_institution	Sep. 30, 2018 USD ($)	Dec. 31, 2018 financial_institution
Schedule of Accounting Policies [Line Items]
Renewal term			1 year
Number of reportable segments | segment			2
Amortization period of inventories and supplies			24 months
Goodwill and intangible asset impairment			$ 0	$ 0
Revenue	$ 455,606,000	$ 505,500,000	1,393,818,000	1,507,649,000
Costs of services provided	398,404,000	438,262,000	1,226,154,000	1,343,545,000
Investment and other income, net	$ 733,000	3,239,000	$ 7,329,000	7,624,000
Number of financial institutions holding cash and cash equivalents and marketable securities | financial_institution	1		1		1
Prior period adjustment
Schedule of Accounting Policies [Line Items]
Revenue		(1,400,000)		(4,800,000)
Costs of services provided		(900,000)		(3,200,000)
Investment and other income, net		$ 500,000		$ 1,600,000
Minimum
Schedule of Accounting Policies [Line Items]
Cancellation notice period			30 days
Initial period preceding cancellation notice			60 days
Maximum
Schedule of Accounting Policies [Line Items]
Cancellation notice period			90 days
Initial period preceding cancellation notice			120 days