CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Operating activities:
Net income	$ 7,584	$ 476
Adjustments to reconcile net income to net cash (used in) provided by operating activities:
Depreciation and amortization expense	12,266	8,969
Amortization of bond premium	74	86
Deferred income taxes	3,112	(118)
Non-cash interest on leased facility	230	229
Stock-based compensation	5,842	4,910
Changes in operating assets and liabilities:
Accounts receivable, net of allowance for doubtful accounts	(28,935)	5,519
Prepaid expenses and other current assets	816	4,499
Other assets	465	(384)
Accounts payable	(3,388)	(2,639)
Accrued expenses	(8,743)	(11,126)
Contingent consideration obligation	1,611	241
Excess tax benefit from the exercise of stock options	(385)
Other liabilities	1,249	1,247
Deferred revenues	(3,204)	3,325
Net cash (used in) provided by operating activities	(11,406)	15,234
Investing activities:
Purchases of fixed assets	(8,044)	(10,964)
Purchases of marketable securities available-for-sale	(1,244)	(13)
Maturities of marketable securities available-for-sale	315	4,791
Net cash used in investing activities	(8,973)	(6,186)
Financing activities:
Proceeds from the exercise of stock options	3,273	6,212
Excess tax benefit from the exercise of stock options	385
Proceeds from the sale of treasury stock in connection with an employee stock purchase plan	740	670
Repayments of capital obligations	(324)	(760)
Net cash provided by financing activities	4,074	6,122
Effect of exchange rate changes on cash	64	(82)
Net (decrease) increase in cash and cash equivalents	(16,241)	15,088
Cash and cash equivalents at beginning of period	63,512	36,028
Cash and cash equivalents at end of period	47,271	51,116
Supplemental disclosures of cash flow information:
Cash paid for income taxes	$ 717	$ 337