CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 73,185	$ 39,122	$ 13,425
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	9,240	8,574	7,442
Amortization	29,561	37,900	50,672
Stock-based compensation expense	6,499	4,463	9,815
Amortization of debt issuance costs and discount	615	662	2,576
Loss on extinguishment of debt	0	0	10,726
Deferred income tax provision (benefit)	3,942	3,237	(9,006)
Amortization and adjustment of deferred credit	(7,712)	(8,781)	0
Other	1,653	(673)	(1,019)
Changes in assets and liabilities:
Accounts receivable and unbilled, net	(27,047)	(2,898)	(13,727)
Prepaid expenses and other current assets	(1,241)	(3,533)	(3,661)
Accounts payable	1,342	4,816	691
Accrued expenses	29,029	(1,313)	4,516
Pre-funded study costs	0	5,292	5,400
Advanced billings	35,593	7,735	14,723
Other assets and liabilities, net	1,925	2,782	(841)
Net cash provided by operating activities	156,584	97,385	91,732
CASH FLOWS FROM INVESTING ACTIVITIES:
Property and equipment expenditures	(16,024)	(11,724)	(13,537)
Acquisition of intangibles	0	(569)	0
Other	(949)	56	115
Net cash used in investing activities	(16,973)	(12,237)	(13,422)
CASH FLOWS FROM FINANCING ACTIVITIES:
Payment for common stock issuance costs	0	0	(2,719)
Proceeds from stock option exercises	2,489	1,812	537
Repurchases of common stock	0	(155,583)	0
Excess tax benefit from stock-based compensation	0	0	25
Proceeds from issuance of debt, net of original issue discount	0	0	164,506
Payment of debt	(72,188)	(12,375)	(390,060)
Proceeds from revolving loan	0	100,000	0
Payments on revolving loan	(70,000)	(30,000)	0
Debt issuance costs	0	0	(1,802)
Payment of deemed landlord liability	(1,881)	(1,682)	(1,525)
Payment on debt extinguishment	0	0	(548)
Proceeds from common stock issued, net	0	0	173,578
Net cash used in financing activities	(141,580)	(97,828)	(58,008)
EFFECT OF EXCHANGE RATES ON CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	(1,241)	1,765	(632)
(DECREASE) INCREASE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH	(3,210)	(10,915)	19,670
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH — Beginning of period	26,492	37,407	17,737
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH — End of period	23,282	26,492	37,407
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION—
Cash paid during the period for income taxes	23,311	17,180	17,654
Cash paid during the period for interest	7,589	6,888	16,895
Acquisition of property and equipment—non-cash	$ 1,551	$ 678	$ 1,687