Segment Information (Total Revenue to Unaffiliated Customers by Geographic Area, Based on Location of Customer) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Revenue:
Total revenue	$ 31,382	$ 31,527	$ 31,003	$ 31,105	$ 29,746	$ 28,527	$ 26,901	$ 24,721	$ 125,017	$ 109,895	$ 87,973
North America [Member]
Revenue:
Total revenue									75,419	65,336	55,836
Europe [Member]
Revenue:
Total revenue									30,624	27,180	20,314
Japan [Member]
Revenue:
Total revenue									7,902	6,497	5,949
Asia Pacific [Member]
Revenue:
Total revenue									10,109	10,095	5,174
Other [Member]
Revenue:
Total revenue									$ 963	$ 787	$ 700