Leases (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Leased Assets [Line Items]
Total lease expense	$ 4,600,000	$ 3,900,000	$ 3,600,000
Rental income	3,100,000	446,000
Future minimum lease payments under operating lease
2015	2,558,000
2016	2,204,000
2017	1,950,000
2018	1,813,000
2019	1,697,000
2020 and beyond	904,000
Total minimum lease payments	11,126,000
Minimum lease receipts	(1,388,000)
Total net minimum lease payments	$ 9,738,000
Office and laboratory space - Germany [Member]
Operating Leased Assets [Line Items]
Operating lease expiration date	Jun. 30, 2015
Office space - England [Member]
Operating Leased Assets [Line Items]
Operating lease expiration date	Nov. 30, 2016
Office and laboratory space - Maryland [Member]
Operating Leased Assets [Line Items]
Operating lease expiration date	Dec. 31, 2016
Annual escalation percentage (in hundredths)	3.00%
Office and laboratory space - Washington [Member]
Operating Leased Assets [Line Items]
Operating lease expiration date	Apr. 30, 2020