Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income	$ 15,140	$ 17,651	$ 11,996
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and asset write offs	6,648	7,812	8,350
Amortization of intangible assets	781	831	891
Net losses from investments	479	805	18
Deferred income taxes	6,425	2,602	(985)
Stock-based compensation	8,490	7,976	8,347
Amortization of premium on investments	207	345	693
Foreign currency (gains) losses	632	(81)	38
Changes in assets and liabilities
Accounts receivable	(10,327)	7,963	(718)
Deferred commissions	(1,679)	1,477	225
Prepaid expenses and other current assets	(4,146)	861	1,482
Accounts payable	(1,600)	1,317	(357)
Accrued expenses and other liabilities	7,857	58	6,116
Deferred revenue	8,586	(5,140)	(2,120)
Net cash provided by operating activities	37,493	44,477	33,976
Cash flows from investing activities:
Purchases of property and equipment	(7,861)	(4,140)	(3,931)
Purchases of marketable investments	(31,910)	(36,763)	(20,587)
Proceeds from sales and maturities of marketable investments	38,458	23,086	26,960
Other investing activity	343	(48)	347
Net cash provided by (used in) investing activities	(970)	(17,865)	2,789
Cash flows from financing activities:
Dividends paid on common stock	(13,631)	(12,987)	(12,179)
Repurchases of common stock	(39,967)	(1,791)	(20,931)
Proceeds from issuance of common stock under employee equity incentive plans	18,506	16,734	3,347
Taxes paid related to net share settlements of stock-based compensation awards	(2,527)	(2,069)	(1,459)
Net cash used in financing activities	(37,619)	(113)	(31,222)
Effect of exchange rate changes on cash and cash equivalents	3,928	(2,872)	(1,862)
Net increase in cash and cash equivalents	2,832	23,627	3,681
Cash and cash equivalents, beginning of year	76,958	53,331	49,650
Cash and cash equivalents, end of year	79,790	76,958	53,331
Supplemental disclosure of cash flow information:
Cash paid for income taxes	$ 10,443	$ 8,507	$ 6,425