Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating activities
Net income (loss)	$ (51,003)	$ 2,495	$ 54,455
Adjustment to reconcile net income (loss) to net cash (used in) provided by operating activities:
Depreciation and amortization	18,674	16,266	12,796
Share-based compensation	27,204	18,147	11,111
Provision for doubtful accounts	209	346	231
Amortization of premiums on marketable securities	3,035	1,889	323
Deferred income tax (benefit) expense	(33,700)	2,592	(37,612)
Other	288	126	21
Change in operating assets and liabilities:
Trade and other receivables	(7,648)	(933)	(3,127)
Prepaid expenses and other current assets	(4,463)	(880)	(1,080)
Other non-current assets	389	280	328
Accounts payable	12,471	9,029	518
Accrued expenses and other liabilities	8,755	31,655	6,920
Deferred revenue	21,197	26,100	28,115
Other non-current liabilities	782	2,066	4,374
Net cash provided by (used in) operating activities	(3,810)	109,178	77,373
Investing activities
Acquisition of businesses, net of cash acquired	(12,797)	0	(42,369)
Acquisition of property and equipment, including capitalization of internal use software	(14,156)	(14,574)	(10,417)
Acquisition of intangible assets	(925)	0	0
Purchases of marketable securities	(225,232)	(135,178)	(50,775)
Sale and maturities of marketable securities	156,230	56,060	1,353
Premiums paid for company-owned life insurance policies	(4,337)	(4,337)	0
Net cash used in investing activities	(101,217)	(98,029)	(102,208)
Financing activities
Proceeds from stock based compensation plans	11,787	12,241	15,425
Proceeds from warrant exercises	0	375	0
Payments for employee tax withholdings related to restricted stock units and awards	(2,905)	(1,107)	(436)
Payments for debt issuance costs	(185)	0	(440)
Net cash provided by financing activities	8,697	11,509	14,549
Net increase (decrease) in cash and cash equivalents	(96,330)	22,658	(10,286)
Cash and cash equivalents at beginning of year	146,569	123,911	134,197
Cash and cash equivalents at end of year	50,239	146,569	123,911
Cash paid (refunded) during the period for:
Interest	323	161	267
Income taxes	910	(235)	1,121
Supplemental information for non-cash investing activities:
Accrued capital expenditures	2,676	1,835	1,300
Property and equipment acquired through leasehold incentives	$ 822	$ 284	$ 0