Liability for Unpaid Claims - Summary of Liability for Unpaid Health Claims (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Activity in the Liability for Unpaid Health Claims
Balance at beginning of period	$ 143,128	$ 137,120
Incurred related to:
Current year	135,377	126,897
Prior years	(4,024)	(316)
Total incurred	131,353	126,581
Paid related to:
Current year	54,241	52,621
Prior years	77,555	76,421
Total paid	131,796	129,042
Balance at end of period	$ 142,685	$ 134,659