Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash flows from operating activities:
Net income	$ 26,975	$ 8,084
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Deferred income taxes	1,877	(5,405)
Depreciation and amortization	20,774	20,042
Stock-based compensation expense	2,083	1,074
Amortization of debt issuance costs	645	1,348
Accretion of asset retirement obligations	48	46
Changes in operating assets and liabilities:
Restricted cash	1,871	(1,518)
Accounts receivable	5,663	12,266
Other assets	(2,612)	7,493
Customer deposits	(1,871)	1,518
Accrued compensation	(29,210)	(8,452)
Accounts payable and accrued other expenses	(841)	(2,225)
Estimated liability for refunds and appeals	(774)	2,262
Other long-term liabilities	247	144
Other	(303)	(324)
Net cash provided by operating activities	24,572	36,353
Cash flows from investing activities:
Expenditures for property and equipment	(9,660)	(9,467)
Other investing activities		2
Net cash used in investing activities	(9,660)	(9,465)
Cash flows from financing activities:
Proceeds from exercise of stock options	7,363	16
Purchase of treasury shares	(3)
Repayment of debt	(4,500)	(2,025)
Net cash provided by (used in) financing activities	2,860	(2,009)
Effect of foreign exchanges on cash and cash equivalents	51	8
Net increase in cash and cash equivalents	17,823	24,887
Cash and cash equivalents at beginning of period	110,635	149,365
Cash and cash equivalents at end of the period	128,458	174,252
Supplemental disclosures of cash flow information:
Cash paid for income taxes	649	590
Cash paid for interest	7,587	14,565
Noncash investing activities (accrued property and equipment purchases)	$ 6,738	$ 9,052