Selected Quarterly Financial Data (Unaudited) - Stock Based Compensation - Allocated Share-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended									6 Months Ended			9 Months Ended			12 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2013	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense, Total	$ 3,341	$ 3,157	$ 2,974	$ 1,790	$ 1,992	$ 1,282	$ 1,430	$ 2,541	$ 1,703	$ 6,131	$ 3,275	$ 4,244	$ 9,471	$ 5,065	$ 5,674	$ 13,100	$ 7,800	$ 7,100
Stock Options And Employee Stock Purchase Plan Espp [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense, Total	2,231	2,415	2,252	1,505	1,900	1,221	1,326	2,191	1,639	4,667	3,122	3,830	6,898	4,627	5,156
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense, Total	$ 1,110	$ 742	$ 722	$ 285	$ 92	$ 61	$ 104	$ 350	$ 64	$ 1,464	$ 153	$ 414	$ 2,573	$ 438	$ 518	$ 3,900	$ 1,200	$ 600