CONDENSED CONSOLIDATED STATEMENTS OF INCOME (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Income Statement [Abstract]
Revenue	$ 41,085	$ 38,496	$ 83,124	$ 72,845
Cost of revenue	6,016	6,080	12,025	9,738
Cost of revenue-amortization of acquired technology	1,139	1,085	2,277	1,880
Total cost of revenue	7,155	7,165	14,302	11,618
Gross profit	33,930	31,331	68,822	61,227
Operating expenses:
Marketing and selling	10,392	8,720	20,311	17,991
Research and development	4,891	4,588	9,863	8,932
General and administrative	4,980	4,698	9,685	9,625
Amortization of other intangible assets	1,487	1,431	2,977	2,652
Total operating expenses	21,750	19,437	42,836	39,200
Income from operations	12,180	11,894	25,986	22,027
Other (income) expense:
Interest expense	313	553	731	1,004
Interest income	(5)	(9)	(5)	(16)
Loss on foreign exchange	263	10	840	277
Gain on derivatives		(205)		(79)
Other income, net	(1)	(3)	(37)	(14)
Total other expense	570	346	1,529	1,172
Income before provision for income taxes	11,610	11,548	24,457	20,855
Provision for income taxes	4,299	4,133	8,530	7,720
Net income	7,311	7,415	15,927	13,135
Net income available to common stockholders-basic	7,182	7,286	15,658	12,921
Net income available to common stockholders-diluted	$ 7,185	$ 7,286	$ 15,665	$ 12,921
Net income per common share:
Basic	$ 0.19	$ 0.20	$ 0.42	$ 0.36
Diluted	$ 0.18	$ 0.19	$ 0.40	$ 0.34
Weighted average number of shares:
Basic	37,725,082	36,046,725	37,415,514	36,164,567
Diluted	39,029,653	37,423,532	38,758,807	37,589,957
Dividends declared per common share	$ 0.06		$ 0.12