CONSOLIDATED STATEMENTS OF CASH FLOW (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Operating activities:
Net income and comprehensive income	$ 50,516	$ 47,785	$ 40,092
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	54,836	22,435	15,908
Stock-based compensation expense	9,116	8,376	7,544
Excess tax benefit from exercised stock options	(12,433)	(12,051)	(12,581)
Deferred income taxes	(6,323)	1,818	2,316
Allowance for doubtful debts	3,654	359	197
Change in fair value of contingent consideration	(2,300)	(273)	273
Loss on disposal of fixed assets	290	267	23
Changes in assets and liabilities:
Accounts receivable	(36,382)	(31,931)	(9,657)
Prepaid expenses	(7,670)	(1,081)	664
Prepaid income taxes	14,326	14,288	13,282
Other current assets	667	(538)	(304)
Other assets	(127)	113	90
Accounts payable, accrued expenses and other liabilities	462	(218)	4,078
Estimated liability for appeals	14,407	7,380
Net cash provided by operating activities	83,039	56,729	61,925
Investing activities:
Investment in certificate of deposit		(4,809)
Proceeds from redemption of certificate of deposit	4,809
Purchases of property and equipment	(25,222)	(18,477)	(15,603)
Purchase of building and land			(9,886)
Investment in common stock	(3,024)
Acquisitions, net	(12,393)	(350,578)	(26,149)
Investment in capitalized software	(2,244)	(1,857)	(2,023)
Net cash used in investing activities	(38,074)	(375,721)	(53,661)
Financing activities:
Repayment of term loan	(17,500)	(39,480)
Proceeds from term loan		337,292
Deferred financing costs		(292)
Purchases of treasury stock	(10,617)
Payments on contingent consideration	(250)
Proceeds from exercise of stock options	11,973	12,744	9,128
Payments on capital lease obligations	(996)
Payments of tax withholdings on behalf of employees for net-share settlement for stock-based compensation	(1,784)	(1,156)
Excess tax benefit from exercised stock options	12,433	12,051	12,581
Net cash (used in )/provided by financing activities	(6,741)	321,159	21,709
Net increase in cash and cash equivalents	38,224	2,167	29,973
Cash and cash equivalents at beginning of year	97,003	94,836	64,863
Cash and cash equivalents at end of year	135,227	97,003	94,836
Supplemental disclosure of cash flow information:
Cash paid for income taxes	20,490	17,474	10,949
Cash paid for interest	13,236	109	70
Supplemental disclosure of noncash investing activities:
Tenant improvement allowance			202
Accrued property and equipment purchases	4,439	5,294	2,804
Accrued acquisition related contingent consideration			2,573
Issuance of replacement awards in connection with HDI acquisition		3,799
Equipment purchased through capital leases	$ 2,127