Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Allowance for uncollectible accounts	$ 21,775	$ 19,846
Liabilities and Equity [Abstract]
Preferred stock, par value (in USD per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	11,000,000	11,000,000
Preferred stock, shares outstanding (in shares)	0	0
Stockholders' Equity Attributable to Parent [Abstract]
Common stock, par value (in USD per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	175,000,000	175,000,000
Common stock, shares outstanding (in shares)	80,764,000	82,937,000