CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Operating activities:
Net income	$ 44,314	$ 32,297
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	33,158	34,961
Amortization of debt issuance costs	1,487	1,610
Stock-based compensation expense	19,460	17,670
Deferred income tax expense, net	3,434	3,474
Provision for losses on accounts receivable	2,349	5,108
Changes in operating assets and liabilities, net of acquisitions:
Accounts receivable	(5,177)	(10,868)
Prepaid expenses and other current assets	(7,887)	(2,616)
Deposits and other assets	(103)	482
Accounts payable and other liabilities	605	4,956
Deferred revenue	3,723	(380)
Net cash provided by operating activities	95,363	86,694
Investing activities:
Proceeds from sale and settlement of investments	0	4,700
Purchases of property and equipment and other assets	(12,674)	(7,394)
Acquisitions, net of cash acquired	(45,068)	(10,795)
Net cash used in investing activities	(57,742)	(13,489)
Financing activities:
Payments of long-term debt	(35,000)	(20,000)
Repurchase of restricted stock to satisfy tax withholding obligations	(13,456)	(13,967)
Proceeds from exercise of stock options and employee stock purchase plan	7,683	3,837
Net cash used in financing activities	(40,773)	(30,130)
Effect of foreign currency exchange rates on cash and cash equivalents	567	(742)
Net increase (decrease) in cash and cash equivalents	(2,585)	42,333
Cash and cash equivalents at the beginning of period	567,223	421,818
Cash and cash equivalents at the end of period	$ 564,638	$ 464,151