Liability for Unpaid Claims - Summary of Liability for Unpaid Health Claims (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Activity in the Liability for Unpaid Health Claims
Balance at beginning of period	$ 143,128	$ 137,120
Incurred related to:
Current year	393,747	388,998
Prior years	(10,745)	(5,710)
Total incurred	383,002	383,288
Paid related to:
Current year	279,563	275,388
Prior years	103,010	102,435
Total paid	382,573	377,823
Balance at end of period	$ 143,557	$ 142,585