Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net income	$ 24,067	$ 45,398
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	10,393	8,172
Amortization	30,684	28,031
Amortization of debt issuance costs	399	294
Amortization of commissions	2,210	0
Stock-based compensation expense	14,799	17,988
Loss on disposal of fixed assets	172	98
Provision for doubtful accounts	1,016	90
Deferred taxes	0	592
Realized (gain) loss on investments	0	(4)
Accrued interest on debt securities	(311)	(95)
Changes in operating assets and liabilities:
Receivables	21,976	(66,166)
Prepaid expenses and other current assets	14,058	130
Other assets	(20,347)	(1,709)
Accounts payable and accrued expenses	3,552	15,533
Customer obligations	(30,848)	79,082
Other liabilities	4,048	1,683
Net cash provided by operating activities	75,868	129,117
Cash flows from investing activities:
Purchases of property and equipment	(27,658)	(28,489)
Purchases of short-term investments	(154,696)	(99,445)
Proceeds from sales of short-term investments	7,639	5,398
Proceeds from maturities of short-term investments	88,435	0
Purchases of intangible assets	(209)	(2,107)
Net cash used in investing activities	(86,489)	(124,643)
Cash flows from financing activities:
Proceeds from public stock offering, net of underwriting discounts, commissions and other costs	0	130,832
Proceeds from exercise of common stock options	1,395	10,834
Proceeds from issuance of common stock under Employee Stock Purchase Plan	869	2,172
Payments of debt issuance costs	(500)	(1,851)
Payments of debt principal	0	(2,500)
Payments for treasury stock acquired	0	(7,935)
Payments of capital lease	(233)	(224)
Taxes paid related to net share settlement of stock-based compensation arrangements	(218)	(8,832)
Net cash provided by financing activities	1,313	122,496
Net (decrease) increase in cash and cash equivalents, unrestricted and restricted	(9,308)	126,970
Cash and cash equivalents at beginning of period, unrestricted and restricted	779,677	672,609
Cash and cash equivalents at end of period, unrestricted and restricted	770,369	799,579
Cash paid during the period for:
Interest	6,444	4,672
Income taxes	1,979	2,940
Noncash financing and investing activities:
Property and equipment, accrued but not paid	1,853	3,732
Contingent payment, accrued but not paid	0	2,060
Property and equipment financed under capital lease	$ 142	$ 263