Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities
Net income	$ 4,639	$ 2,704	$ 1,051
Reconciliation of net income to net cash provided by operating activities
Deferred income taxes	(38)	1,031	443
Depreciation and amortization of property and equipment	6,265	5,714	4,893
Amortization of intangible assets	3,307	2,856	3,158
Provision for doubtful accounts	1,271	717	479
Stock-based compensation	6,379	5,396	4,203
Changes in assets and liabilities, net of effects of acquisitions
Accounts receivable	(3,517)	(3,890)	(1,150)
Deferred costs	(3,023)	(4,590)	(2,184)
Other current assets	(2,037)	(719)	2,593
Other non-current assets			28
Accounts payable	(1,569)	1,271	(59)
Accrued compensation	1,295	1,568	1,943
Accrued expenses	(461)	1,365	(108)
Deferred revenue	587	2,440	1,309
Deferred rent	1,331	925	1,644
Net cash provided by operating activities	14,429	16,788	18,243
Cash flows from investing activities
Business acquisitions, net of cash acquired		(12,595)
Purchases of property and equipment	(8,757)	(7,582)	(5,701)
Purchases of marketable securities	(22,527)
Net cash used in investing activities	(31,284)	(20,177)	(5,701)
Cash flows from financing activities
Net proceeds from stock offerings			47,738
Stock offering costs			(169)
Net proceeds from exercise of options to purchase common stock	4,440	1,886	3,735
Excess tax benefit from exercise of options to purchase common stock	2,336	261	156
Net proceeds from employee stock purchase plan	1,478	1,338	1,242
Net cash provided by financing activities	8,254	3,485	52,702
Effect of foreign currency exchange rate changes	(656)	(595)
Net increase (decrease) in cash and cash equivalents	(9,257)	(499)	65,244
Cash and cash equivalents at beginning of period	130,795	131,294	66,050
Cash and cash equivalents at end of period	121,538	130,795	131,294
Supplemental disclosure of cash flow information
Cash paid for income taxes	$ 114	113	$ 55
Non-cash financing activities:
Common stock issued for business acquisitions		$ 2,203