Consolidated Statements of Cash Flows $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Cash flows from operating activities
Net income	$ 44,841	$ 73,633	$ 45,404
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	79,566	73,948	70,491
Provision for doubtful accounts and sales returns	6,890	11,686	3,730
Stock-based compensation expense	48,274	40,631	32,638
Deferred taxes	(619)	(17,814)	5,415
Amortization of deferred financing costs and discount	752	838	958
Other non-cash adjustments	(1,912)	504	(864)
Changes in operating assets and liabilities, net of acquisition and disposal of businesses:
Accounts receivable	2,166	(15,821)	(13,007)
Prepaid expenses and other assets	(5,217)	(9,550)	(8,495)
Trade accounts payable	9,487	1,024	3,689
Accrued expenses and other liabilities	(2,027)	(4,973)	(751)
Deferred revenue	19,184	22,184	14,420
Net cash provided by operating activities	201,385	176,290	153,628
Cash flows from investing activities
Purchase of property and equipment	(14,719)	(10,208)	(17,694)
Capitalized software development costs	(37,629)	(28,345)	(26,359)
Purchase of net assets of acquired companies, net of cash and restricted cash acquired	(44,943)	(146,789)	(3,377)
Purchase of derivative instruments	0	(568)	0
Proceeds from settlement of derivative instruments	0	1,030	0
Other investing activities	(500)	0	0
Net cash used in investing activities	(97,791)	(184,880)	(47,430)
Cash flows from financing activities
Proceeds from issuance of debt	270,900	774,500	227,200
Payments on debt	(322,476)	(679,119)	(293,575)
Debt issuance costs	0	(3,085)	0
Employee taxes paid for withheld shares upon equity award settlement	(27,685)	(23,962)	(15,376)
Proceeds from exercise of stock options	11	15	16
Change in due to customers	(188,502)	226,717	96,000
Change in customer funds receivable	(844)	6,644	0
Dividend payments to stockholders	(23,312)	(23,069)	(22,811)
Net cash (used in) provided by financing activities	(291,908)	278,641	(8,546)
Effect of exchange rate on cash, cash equivalents, and restricted cash	(2,014)	(550)	2,622
Net (decrease) increase in cash, cash equivalents, and restricted cash	(190,328)	269,501	100,274
Cash, cash equivalents, and restricted cash, beginning of year	640,174	370,673	270,399
Cash, cash equivalents, and restricted cash, end of year	449,846	640,174	370,673
Cash (paid) received during the year for:
Interest	(15,261)	(10,614)	(9,608)
Taxes, net of refunds	7,138	(5,613)	(1,340)
Non-cash investing and financing activities:
Purchase of equipment and other assets included in accounts payable	(882)	(1,546)	(3,155)
Acquired restricted cash liabilities due to customers	0	31,644	$ 0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	30,866	29,830
Restricted cash due to customers	418,980	610,344
Total cash, cash equivalents and restricted cash in the statement of cash flows	$ 449,846	$ 640,174