Liability for Unpaid Claims - Summary of Liability for Unpaid Health Claims (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Activity in the Liability for Unpaid Health Claims
Balance at beginning of period	$ 143,128	$ 137,120
Incurred related to:
Current year	264,648	258,640
Prior years	(8,364)	(3,789)
Total incurred	256,284	254,851
Paid related to:
Current year	164,271	160,740
Prior years	94,676	94,284
Total paid	258,947	255,024
Balance at end of period	$ 140,465	$ 136,947