CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Cash flows from operating activities:
Net income	$ 15,364	$ 13,662
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	5,096	5,516
Deferred taxes	2,669	3,352
Compensation expense related to share-based compensation plans	1,882	1,637
(Gain) loss on sale of assets	(214)	1
Excess tax benefits from share-based compensation	(3)	(83)
Changes in operating assets and liabilities:
Restricted investments	(181)	(1,509)
Accounts receivable, net	(11,893)	(14,043)
Prepaid taxes	(30)	2,243
Prepaid expenses and other current assets	2,227	2,205
Other assets	(146)	445
Accounts payable	16,230	8,377
Accrued expenses	(2,801)	22
Non-current liabilities	(198)	1,010
Net cash provided by operating activities	28,002	22,835
Cash flows from investing activities:
Proceeds from sale of equipment	734	52
Purchases of property and equipment	(9,456)	(17,013)
Cash used in acquisitions		(150)
Net cash used in investing activities	(8,722)	(17,111)
Cash flows from financing activities:
Proceeds from stock options exercised	42	16
Stock tendered for payments of withholding taxes	(2,469)	(1,665)
Purchase of treasury stock	(903)
Capital lease payments	(560)	(546)
Excess tax benefits from share-based compensation	98	74
Net cash used in financing activities	(3,792)	(2,121)
Effect of exchange rate changes on cash and cash equivalents	3	1
Net increase in cash and cash equivalents	15,491	3,604
Cash and cash equivalents beginning of period	70,760	49,091
Cash and cash equivalents end of period	86,251	52,695
Supplemental disclosures of cash paid for:
Interest	311	333
Income taxes	$ 3,438	$ 472