Condensed Consolidated Statement Of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities:
Net income	$ 57,196	$ 63,713
Adjustments to reconcile net earnings to net cash provided by operating activities:
Depreciation and amortization	79,225	58,233
Accretion and amortization of discount and premium of investments	0	646
Amortization of financing costs and discounts	6,307	4,777
Share-based compensation	9,177	6,248
Provision for doubtful accounts	5,623	5,009
Deferred income taxes	(3,679)	(2,064)
Decrease (increase) in:
Accounts receivable	11,195	3,763
Prepaid expenses and other current assets	2,527	1,534
Other assets	(105)	(1,894)
(Decrease) increase in:
Accounts payable and accrued expenses	(55,047)	(15,480)
Income taxes payable	(4,464)	2,034
Deferred revenue	1,817	(2,699)
Liability for uncertain tax positions	(4)	4,440
Other	1,887	3,792
Net cash provided by operating activities	111,655	132,052
Cash flows from investing activities:
Maturity of available-for-sale investments	0	112,631
Purchase of available-for-sale investments	(5)	(47,207)
Purchases of property and equipment	(18,945)	(9,186)
Acquisition of businesses, net of cash received	(36,430)	(76,725)
Purchases of intangible assets	(768)	(1,815)
Net Cash Provided by (Used in) Investing Activities	(56,148)	(22,302)
Cash flows from financing activities:
Proceeds from Issuance of Long-term Debt	636,178	0
Proceeds from Lines of Credit	44,981	0
Repayments of Lines of Credit	(225,000)	0
Repurchases of common stock and restricted stock	(6,738)	(3,356)
Issuance of common stock under employee stock purchase plan	133	123
Exercise of stock options	1,051	1,911
Dividends paid	(35,707)	(32,202)
Deferred payments for acquisitions	(3,339)	(16,550)
Proceeds from (Payments for) Other Financing Activities	(36)	843
Net Cash Provided by (Used in) Financing Activities	411,523	(49,231)
Effect of exchange rate changes on cash, cash equivalents and restricted cash	5,576	(2,295)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease)	472,606	58,224
Disposal Group, Including Discontinued Operation, Cash and Cash Equivalents	813
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	595,743	$ 313,754
Cash and Cash Equivalents, at Carrying Value	$ 330,743