CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net income	$ 74,805	$ 70,949	$ 51,558
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	44,712	37,042	29,380
Impairment of software			11,881
Deferred taxes	13,801	16,378	24,501
Compensation expense related to share-based compensation plans	8,479	7,833	8,258
Gain on sale of assets	(573)	(129)	(46)
Excess tax benefits from share based compensation	(733)	(81)
Changes in operating assets and liabilities:
Restricted investments	231	836	(1,190)
Accounts receivable, net	(87,629)	36,373	(28,621)
Prepaid taxes	66	14,575	(14,533)
Prepaid expenses and other current assets	1,099	(3,401)	(1,621)
Other assets	570	(805)	(2,047)
Accounts payable	35,709	(25,736)	20,370
Accrued expenses	9,238	20,505	367
Non-current liabilities	2,698	(2,642)	284
Net cash provided by operating activities	102,473	171,697	98,541
Cash flows from investing activities:
Proceeds from sale of equipment	2,061	2,309	612
Purchases of property and equipment	(107,409)	(83,042)	(119,171)
Net cash used in investing activities	(105,348)	(80,733)	(118,559)
Cash flows from financing activities:
Proceeds from issuance of debt	62,155	64,442	91,084
Repayments of long-term debt	(34,767)	(23,217)	(7,251)
Stock tendered for payments of withholding taxes	(2,489)	(2,916)	(3,195)
Purchase of treasury stock	(100,000)	(28,823)	(18,024)
Capital lease payments	(2,634)	(2,534)	(2,449)
Excess tax benefits from share-based compensation	372	195	652
Net cash (used in) provided by financing activities	(77,363)	7,147	60,817
Effect of exchange rate changes on cash and cash equivalents	(107)	(131)	6
Net (decrease) increase in cash and cash equivalents	(80,345)	97,980	40,805
Cash and cash equivalents beginning of the year	207,749	109,769	68,964
Cash and cash equivalents end of the year	127,404	207,749	109,769
Supplemental disclosures of cash paid for:
Interest	3,665	2,977	1,532
Income taxes	$ 33,233	$ 6,990	$ 20,189