CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Operating activities:
Net income	$ 78,491	$ 55,498
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	48,277	53,041
Amortization of debt issuance costs	2,157	2,407
Stock-based compensation expense	29,203	26,981
Deferred income tax expense, net	6,087	5,554
Provision for losses on accounts receivable	3,992	6,462
Changes in operating assets and liabilities, net of acquisitions:
Accounts receivable	(15,809)	(13,808)
Prepaid expenses and other current assets	(3,561)	(1,398)
Deposits and other assets	(3,387)	473
Accounts payable and other liabilities	11,888	12,864
Deferred revenue	5,969	386
Net cash provided by operating activities	163,307	148,460
Investing activities:
Proceeds from sale and settlement of investments	0	4,700
Purchases of property and equipment and other assets	(19,754)	(11,692)
Acquisitions, net of cash acquired	(47,767)	(10,443)
Net cash used in investing activities	(67,521)	(17,435)
Financing activities:
Payments of long-term debt	(35,000)	(20,000)
Payments of issuance costs	(643)	0
Repurchase of restricted stock to satisfy tax withholding obligations	(14,309)	(14,573)
Proceeds from exercise of stock options and employee stock purchase plan	9,058	4,791
Net cash used in financing activities	(40,894)	(29,782)
Effect of foreign currency exchange rates on cash and cash equivalents	880	(962)
Net increase in cash and cash equivalents	55,772	100,281
Cash and cash equivalents at the beginning of period	567,223	421,818
Cash and cash equivalents at the end of period	$ 622,995	$ 522,099