Summary of Significant Accounting Policies - Health Care Reform, Cash and Restricted Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2016	Dec. 31, 2017
Health Care Reform
HIF fees	$ 29,900	$ 26,500
Cash and Cash Equivalents
Excess capital and undistributed earnings for regulated subsidiaries included in cash and cash equivalents	63,300
Restricted Assets
Restricted cash and cash equivalents	160,967	$ 81,776	$ 229,013
Restricted short-term investments	363,840		219,111
Restricted deposits (included in other current assets)	43,401		41,121
Restricted long-term investments	2,854		17,287
Total	$ 571,062		$ 506,532
Equity in restricted net assets of consolidated subsidiaries as a percentage of consolidated stockholders' equity	24.60%