Supplementary Financial Data (Unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Supplementary Financial Data (Unaudited)
Net revenue	$ 408,103	$ 388,636	$ 375,847	$ 362,200	$ 352,909	$ 335,985	$ 318,990	$ 301,355	$ 1,534,786	$ 1,309,239	$ 1,025,064
Cost of revenue	133,821	127,404	117,658	113,610	109,012	107,348	102,572	100,081	492,493	419,013	346,341
Gross profit	274,282	261,232	258,189	248,590	243,897	228,637	216,418	201,274
Net income	20,798	16,311	22,367	27,261	29,907	27,197	25,134	23,180	86,737	105,418	76,411
Earnings Per Share, Basic	$ 0.15	$ 0.12	$ 0.16	$ 0.20	$ 0.22	$ 0.20	$ 0.19	$ 0.17	$ 0.63	$ 0.78	$ 0.59
Earnings Per Share, Diluted	$ 0.14	$ 0.11	$ 0.16	$ 0.19	$ 0.21	$ 0.19	$ 0.18	$ 0.17	$ 0.61	$ 0.75	$ 0.55
Cash and cash equivalents	$ 259,733	$ 269,995	$ 263,052	$ 278,627	$ 292,061	$ 257,651	$ 215,448	$ 186,531	$ 259,733	$ 292,061	$ 159,856	$ 104,941