Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flow from operating activities:
Net income	$ 55,322	$ 43,303
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	35,098	35,915
Stock-based compensation	17,936	13,726
Deferred income taxes	1,766	(875)
Changes in operating assets and liabilities	(11,270)	(7,284)
Net cash provided by operating activities	98,852	84,785
Cash flow from investing activities:
Capital expenditures	(19,764)	(15,727)
Capitalization of internally developed software	(11,344)	(24,816)
Additions to other intangibles	(3,936)	(1,124)
Purchases of short-term investments	(137,275)	(52,807)
Sales and maturities of short-term investments	47,634	21,017
Net cash used in investing activities	(124,685)	(73,457)
Cash flow from financing activities:
Proceeds from issuance of common stock	16,622	15,407
Dividends paid	(60,575)	(54,595)
Net cash used in financing activities	(43,953)	(39,188)
Effect of exchange rate changes on cash	(2,759)	5,727
Net change in cash and cash equivalents	(72,545)	(22,133)
Cash and cash equivalents at beginning of period	290,164	285,283
Cash and cash equivalents at end of period	$ 217,619	$ 263,150