CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended					12 Months Ended			24 Months Ended
	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income (loss)	$ 11,291	$ 8,447	$ (21)	$ 3,448		$ 39,122	$ 13,425	$ (8,673)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation						8,574	7,442	6,379
Amortization						37,900	50,672	63,142
Stock-based compensation expense						4,463	9,815	22,324
Amortization of debt issuance costs and discount						662	2,576	2,687
Loss on extinguishment of debt						0	10,726	0
Deferred income tax provision (benefit)						3,237	(9,006)	(12,690)
Impairment of goodwill					$ 9,300	0	0	9,313	$ 0
Amortization and adjustment of deferred credit						(8,781)	0	0
Other						(673)	(1,019)	(242)
Changes in assets and liabilities:
Accounts receivable and unbilled, net						(2,898)	(13,727)	337
Prepaid expenses and other current assets						(3,533)	(3,661)	(181)
Accounts payable						4,816	691	2,481
Accrued expenses						(1,313)	4,516	320
Pre-funded study costs						5,292	5,400	9,981
Advanced billings						7,735	14,723	(7,002)
Other assets and liabilities, net						2,782	(841)	(2,306)
Net cash provided by operating activities						97,385	91,732	85,870
CASH FLOWS FROM INVESTING ACTIVITIES:
Property and equipment expenditures						(11,724)	(13,537)	(6,465)
Acquisition of intangibles						(569)	0	0
Other						56	115	33
Net cash used in investing activities						(12,237)	(13,422)	(6,432)
CASH FLOWS FROM FINANCING ACTIVITIES:
Payment for common stock issuance costs						0	(2,719)	0
Proceeds from stock option exercises						1,812	537	250
Repurchases of common stock						(155,583)	0	0
Excess tax benefit from stock-based compensation						0	25	0
Proceeds from issuance of debt, net of original issue discount						0	164,506	0
Payment of debt						(12,375)	(390,060)	(116,055)
Proceeds from revolving loan						100,000	0	0
Payments on revolving loan						(30,000)	0	0
Debt issuance costs						0	(1,802)	0
Payment of deemed landlord liability						(1,682)	(1,525)	(1,292)
Payment on debt extinguishment						0	(548)	0
Proceeds from common stock issued, net						0	173,578	608
Net cash used in financing activities						(97,828)	(58,008)	(116,489)
EFFECT OF EXCHANGE RATES ON CASH, CASH EQUIVALENTS, AND RESTRICTED CASH						1,765	(632)	(601)
(DECREASE) INCREASE IN CASH, CASH EQUIVALENTS, AND RESTRICTED CASH						(10,915)	19,670	(37,652)
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH — Beginning of period		$ 37,407		$ 17,737		37,407	17,737	55,389	17,737
CASH, CASH EQUIVALENTS, AND RESTRICTED CASH — End of period	$ 26,492		$ 37,407		$ 17,737	26,492	37,407	17,737	$ 26,492
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION—
Cash paid during the period for income taxes						17,180	17,654	10,552
Cash paid during the period for interest						6,888	16,895	24,435
Acquisition of property and equipment—non-cash						$ 678	$ 1,687	$ 176