Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Cash flows from operating activities:
Net income	$ 4,783	$ 3,002
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization expense	3,834	3,182
Bad debt expense	80	175
Loss on disposal of property and equipment	0	4
Stock-based compensation	4,697	3,875
Amortization of premiums and accretion of discounts on investments	208	168
Excess tax benefits from stock-based compensation	(3,095)	(91)
Deferred income taxes	(1,086)	1,362
Changes in operating assets and liabilities:
Accounts receivable	(169)	(5,914)
Prepaid expenses and other assets	573	(670)
Accounts payable	2,026	(3,609)
Accrued liabilities	2,822	1,690
Deferred revenues	2,059	6,782
Other noncurrent liabilities	406	70
Net cash provided by operating activities	17,138	10,026
Cash flows from investing activities:
Purchases of investments	(49,450)	(31,781)
Sales and maturities of investments	52,176	25,977
Purchases of property and equipment	(4,181)	(6,148)
Capitalized software development costs	(118)	(99)
Net cash used in investing activities	(1,573)	(12,051)
Cash flows from financing activities:
Proceeds from exercise of stock options	2,113	3,448
Excess tax benefits from stock-based compensation	3,095	91
Net cash provided by financing activities	5,208	3,539
Net increase in cash and cash equivalents	20,773	1,514
Cash and cash equivalents at beginning of period	91,698	76,504
Cash and cash equivalents at end of period	112,471	78,018
Non-cash investing and financing activities:
Vesting of early exercised common stock options	$ 0	$ 6