Investments in Joint Ventures - S & I Ophthalmic - Additional Information (Details)	1 Months Ended	12 Months Ended
	Oct. 31, 2013 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2017 USD ($) board_seat	Dec. 31, 2016 USD ($)
Schedule Of Investments In Joint Venture [Line Items]
Due from related parties, current			$ 17,913,000	$ 16,793,000
Investment			$ 18,870,000	23,655,000
S & I Ophthalmic, LLC
Schedule Of Investments In Joint Venture [Line Items]
Capital contribution	$ 5,000,000	$ 5,000,000
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, externally selected | board_seat			2
Total number of seats on the joint venture's governing board, internally selected | board_seat			2
S & I Opthalmic, LLC
Schedule Of Investments In Joint Venture [Line Items]
Due from related parties, current			$ 2,598,000
Investor | S & I Ophthalmic, LLC
Schedule Of Investments In Joint Venture [Line Items]
Capital contribution	$ 5,000,000	$ 5,000,000
Membership interest	50.00%
Investments in affiliates | S & I Ophthalmic, LLC
Schedule Of Investments In Joint Venture [Line Items]
Investment				$ 3,236,000