Basis of Presentation, Summary of Significant Accounting Policies and Change in Accounting Principle - Restricted Cash and Restricted Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restricted Cash and Cash Equivalents Items [Line Items]
Total restricted cash and restricted investments	$ 28,340	$ 160,823
Current restricted investments	704	211
Current restricted cash	19,376	154,507
Total current restricted cash and restricted investments	20,080	154,718
Non-current restricted investments	113	607
Non-current restricted cash	8,147	5,498
Total non-current restricted cash and restricted investments	8,260	6,105
Cash and cash equivalents	101,008	228,320
Restricted investments included in restricted cash and restricted investments	(817)	(818)
Total cash and cash equivalents and restricted cash shown in the consolidated statements of cash flows	128,531	388,325	$ 295,363	$ 170,029
Collateral for letters of credit for facility leases
Restricted Cash and Cash Equivalents Items [Line Items]
Total restricted cash and restricted investments	3,610	3,710
Collateral with financial institutions
Restricted Cash and Cash Equivalents Items [Line Items]
Total restricted cash and restricted investments	5,742	34,142
Claims processing services
Restricted Cash and Cash Equivalents Items [Line Items]
Total restricted cash and restricted investments	18,171	122,439
Other
Restricted Cash and Cash Equivalents Items [Line Items]
Total restricted cash and restricted investments	817	532
Collateral with financial institutions, money market funds
Restricted Cash and Cash Equivalents Items [Line Items]
Total restricted cash and restricted investments	1,000	31,200
Bank time deposits
Restricted Cash and Cash Equivalents Items [Line Items]
Total restricted cash and restricted investments	$ 4,700	$ 2,900