Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net income	$ 25,970	$ 54,387	$ 15,902
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	14,011	11,384	8,696
Amortization and impairment	41,456	37,889	37,175
Amortization of debt issuance costs	578	418	159
Amortization of contract costs	2,844	0	0
Provision for doubtful accounts	1,034	558	947
Stock-based compensation expense	18,088	25,649	27,180
Loss on disposal of fixed assets	306	123	273
Accrued interest on debt securities	(493)	(237)	0
Deferred taxes	6,408	9,336	(5,853)
Excess tax benefit related to stock-based compensation arrangements	0	0	(14,806)
Changes in operating assets and liabilities:
Accounts receivable	5,216	(14,692)	(22,088)
Prepaid expenses and other current assets	5,609	(9,514)	7,901
Other assets	(18,558)	(3,145)	(699)
Accounts payable and accrued expenses	8,276	17,387	9,488
Customer obligations	66,732	86,988	207,559
Other liabilities	1,178	1,278	(2,892)
Net cash provided by operating activities	178,655	217,809	268,942
Cash flows from investing activities:
Purchases of property and equipment	(33,535)	(36,787)	(28,319)
Purchases of short-term investments	(157,672)	(208,656)	0
Proceeds from sales of short-term investments	16,049	5,398	0
Proceeds from maturities of short-term investments	114,910	7,500	0
Cash consideration for business acquisitions, net of cash acquired	0	0	(233,965)
Purchases of intangible assets	(209)	(4,658)	(21,120)
Net cash used in investing activities	(60,457)	(237,203)	(283,404)
Cash flows from financing activities:
Proceeds from long-term debt	0	0	169,900
Proceeds from public stock offering	0	135,387	0
Payment of underwriting discounts, commissions and other costs associate with the public offering	0	(4,598)	0
Proceeds from exercise of common stock options	1,395	14,267	16,070
Proceeds from issuance of common stock under Employee Stock Purchase Plan	869	2,681	2,194
Payment of debt issuance / amendment costs	(800)	(1,851)	(207)
Payments of debt principal	0	(2,500)	0
Payment of contingent consideration	0	0	(750)
Payment for treasury stock acquired	0	(7,935)	(9,371)
Payment of capital lease obligations	(299)	(302)	(381)
Taxes paid related to net share settlement of stock-based compensation arrangements	(281)	(9,019)	(6,108)
Excess tax benefit related to stock-based compensation arrangements	0	0	14,806
Net cash provided by financing activities	884	126,130	186,153
Net increase in cash and cash equivalents, unrestricted and restricted	119,082	106,736	171,691
Cash and cash equivalents, unrestricted and restricted, at beginning of the year	779,677	672,941	501,250
Cash and cash equivalents, unrestricted and restricted, at end of the year	898,759	779,677	672,941
Reduction in FBM contingent consideration due to re-negotiated lease
Reduction in FBM contingent consideration due to post-purchase adjustment	8,859	6,462	1,825
Conversion of preferred stock to common stock	2,412	2,958	5,534
Conversion of preferred warrants to common stock warrants
Noncash financing and investing activities:	4,472	2,325	2,412
Property and equipment purchased under capital lease obligations	142	263	835
Capitalized stock-based compensation	$ 319	$ 459	$ 0