Schedule II - Valuation and Qualifying Consolidated Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 6,021	$ 5,151	$ 1,351
Additions Charged to Costs and Expenses	1,218	870	3,800
Deductions	0	0	0
Balance at End of Year	7,239	6,021	5,151
Inventory Valuation Reserve [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	17,305	15,385	13,517
Additions Charged to Costs and Expenses	3,570	1,920	1,868
Deductions	0	0	0
Balance at End of Year	20,875	17,305	15,385
Allowance for Contractual Discounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	111,856	103,601	96,590
Additions Charged to Costs and Expenses	480,645	483,449	439,991
Deductions	474,719	475,194	432,980
Balance at End of Year	117,782	111,856	103,601
Allowance for Uncompensated Care [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	46,310	41,924	41,858
Additions Charged to Costs and Expenses	78,883	88,787	84,470
Deductions	72,678	84,401	84,404
Balance at End of Year	$ 52,515	$ 46,310	$ 41,924