Summary of Significant Accounting Policies - Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Summary of intangible assets
Impairment of intangible assets	$ 4,800	$ 4,800
Gross Carrying Amount		379,828	$ 291,453
Accumulated Amortization		(193,596)	(158,079)
Net Carrying Amount		186,232	133,374
Amortization expense		30,700	$ 29,400	$ 22,800
Estimated amortization expense in future
2017		35,100
2018		30,600
2019		28,500
2020		27,400
2021		$ 26,800
Customer agreements and lists
Summary of intangible assets
Weighted Avg, Remaining Useful Life		6 years 4 months 24 days	6 years 9 months 18 days
Gross Carrying Amount		$ 357,708	$ 274,790
Accumulated Amortization		(181,588)	(148,795)
Net Carrying Amount		$ 176,120	$ 125,995
Customer agreements and lists | Minimum
Summary of intangible assets
Period of amortization of intangible assets acquired		2 years 6 months	2 years 6 months
Customer agreements and lists | Maximum
Summary of intangible assets
Period of amortization of intangible assets acquired		18 years	18 years
Provider networks and other
Summary of intangible assets
Weighted Avg, Remaining Useful Life		4 years 3 months 18 days	4 years 8 months 12 days
Gross Carrying Amount		$ 18,240	$ 16,663
Accumulated Amortization		(12,008)	(9,284)
Net Carrying Amount		$ 6,232	$ 7,379
Provider networks and other | Minimum
Summary of intangible assets
Period of amortization of intangible assets acquired		1 year	1 year
Provider networks and other | Maximum
Summary of intangible assets
Period of amortization of intangible assets acquired		16 years	16 years
AFSC | Trade names
Summary of intangible assets
Carrying Amount		$ 3,880