Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Operating activities:
Net income	$ 24,685	$ 24,440
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation and amortization	11,157	10,515
Share-based compensation	3,094	3,123
(Gain) loss on disposal of property and equipment	(283)	167
Provision for loss on receivables	290	111
Provision for revenue adjustments	1,126	927
Deferred income tax	2,936	1,437
Excess tax benefit for stock options exercised	(2,870)	(206)
Changes in operating assets and liabilities
Accounts receivable	3,196	(5,173)
Prepaid expenses and other current assets	(2,090)	(3,128)
Accounts payable and accrued expenses	(3,991)	(8,293)
Net cash provided by operating activities	37,250	23,920
Investing activities:
Proceeds from disposal of property and equipment	1,048	736
Purchases of property and equipment	(27,994)	(18,318)
Acquisition of businesses, net of cash acquired	(45,328)	0
Other	(60)	(347)
Net cash used in investing activities	(72,334)	(17,929)
Financing activities:
Payments of debt and capital lease obligations	(20,303)	(272)
Proceeds from exercise of stock options	28,179	8,445
Payments of cash dividends	(6,014)	(4,072)
Common stock issued under employee stock purchase plan	137	119
Cash settlement of share-based awards for minimum tax withholdings	(866)	(386)
Excess tax benefit for stock options exercised	2,870	206
Net cash provided by financing activities	4,003	4,040
Net (decrease) increase in cash	(31,081)	10,031
Cash at beginning of period	112,182	58,801
Cash at end of period	$ 81,101	$ 68,832