Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net income	$ 37,584	$ 13,317
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization expense	15,054	12,364
Bad debt expense	353	152
Loss on disposal of property and equipment	3	39
Stock-based compensation	18,522	15,122
Amortization of premiums and accretion of discounts on investments	1,155	617
Excess tax benefits from stock-based compensation	7,880	(4,832)
Deferred income taxes	(17,631)	931
Changes in operating assets and liabilities:
Accounts receivable	317	263
Prepaid expenses and other assets	(405)	(1,196)
Accounts payable	(706)	(877)
Accrued liabilities	747	6,763
Deferred revenues	17,716	10,853
Other non-current liabilities	1,190	1,188
Net cash provided by operating activities	81,779	54,704
Cash flows from investing activities:
Purchases of investments	(198,866)	(180,161)
Sales and maturities of investments	148,025	133,708
Purchases of property and equipment	(26,612)	(18,809)
Purchase of business	(5,753)	0
Net cash used in investing activities	(83,206)	(65,262)
Cash flows from financing activities:
Proceeds from exercise of stock options	22,778	12,529
Excess tax benefits from stock-based compensation	0	4,832
Payments for taxes related to net share settlement of equity awards	(17,571)	(202)
Net cash provided by financing activities	5,207	17,159
Net increase in cash and cash equivalents	3,780	6,601
Cash and cash equivalents at beginning of period	86,737	91,698
Cash and cash equivalents at end of period	90,517
Supplemental cash flow disclosures:
Purchases of property and equipment recorded in accounts payable and accrued liabilities	1,371	2,606
Cash paid for income taxes	$ 1,083	785
Not yet received tenant allowance recorded in other assets, accrued liabilities and other non-current liabilities		$ 0