Investments in Joint Ventures - OvaXon - Additional Information (Details)	1 Months Ended	47 Months Ended
	Jan. 31, 2014 USD ($)	Dec. 31, 2017 USD ($) board_seat	Dec. 31, 2016 USD ($)
Schedule Of Investments In Joint Venture [Line Items]
Investment		$ 18,870,000	$ 23,655,000
OvaXon, LLC
Schedule Of Investments In Joint Venture [Line Items]
Capital contribution	$ 1,500,000	$ 4,350,000
Membership interest	50.00%
Total number of seats on the joint venture's governing board | board_seat		4
Total number of seats on the joint venture's governing board, internally selected | board_seat		2
Total number of seats on the joint venture's governing board, externally selected | board_seat		2
OvaXon, LLC | Investor
Schedule Of Investments In Joint Venture [Line Items]
Capital contribution	$ 1,500,000	$ 4,350,000
Membership interest	50.00%
Investments in affiliates | OvaXon, LLC
Schedule Of Investments In Joint Venture [Line Items]
Investment		$ 146,000	$ 65,000