Summary of Significant Accounting Policies (Details 3) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 item	Dec. 31, 2011	Dec. 31, 2010
Reconciliation of basic to diluted weighted average shares outstanding
Weighted average shares outstanding - basic (in shares)	86,204,000	84,588,000	81,762,000
Dilutive effect of stock options (in shares)	1,901,000	2,715,000	3,498,000
Dilutive effect of restricted stock awards and units (in shares)	260,000	141,000	115,000
Weighted average shares outstanding - diluted (in shares)	88,365,000	87,444,000	85,375,000
Revenue Recognition and estimated liability for appeals
Estimated liability for appeals	$ 21,787	$ 7,380
Revenue Recognition
Number of characteristics for revenue recognition	4
Stock options
Anti-dilutive securities
Anti-dilutive securities excluded from diluted earnings per share calculations (in shares)	566,876	441,863	195,423
Restricted Stock Units
Anti-dilutive securities
Anti-dilutive securities excluded from diluted earnings per share calculations (in shares)	50,300