Condensed Consolidated Statements Of Operations (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Revenues:
Subscriber	$ 88,071	$ 85,298	$ 172,896	$ 158,166
Other	1,394	378	3,221	894
Total revenues	89,465	85,676	176,117	159,060
Cost of revenues (including share-based compensation of $192 and $434 for the three and six months of 2012, respectively, and $246 and $490 for the three and six months of 2011, respectively)	16,187	15,158	32,051	30,950
Gross profit	73,278	70,518	144,066	128,110
Operating expenses:
Sales and marketing (including share-based compensation of $352 and $727 for the three and six months of 2012, respectively, and $351 and $699 for the three and six months of 2011, respectively)	13,860	14,345	28,721	29,856
Research, development and engineering (including share-based compensation of $117 and $233 for the three and six months of 2012, respectively, and $110 and $257 for the three and six months of 2011, respectively)	4,617	3,837	9,106	8,609
General and administrative (including share-based compensation of $1,494 and $3,054 for the three and six months of 2012, respectively, and $1,524 and $2,990 for the three and six months of 2011, respectively)	14,774	14,392	28,603	28,634
Total operating expenses	33,251	32,574	66,430	67,099
Operating earnings	40,027	37,944	77,636	61,011
Interest and other income (expense), net	809	299	91	(28)
Earnings before income taxes	40,836	38,243	77,727	60,983
Income tax expense	9,648	9,729	18,000	1,534
Net earnings	$ 31,188	$ 28,514	$ 59,727	$ 59,449
Net earnings per common share:
Basic	$ 0.68	$ 0.63	$ 1.28	$ 1.31
Diluted	$ 0.67	$ 0.61	$ 1.27	$ 1.27
Weighted average shares outstanding:
Basic	45,373,930	45,399,940	45,887,185	45,247,381
Diluted	45,569,564	46,723,792	46,203,491	46,663,866
Cash dividends paid per common share	$ 0.22	$ 0.00	$ 430.00	$ 0