Investments - Additional Information (Detail)	1 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($) Investment
Investments Debt And Equity Securities [Abstract]
Number of investments in marketable equity securities | Investment			2
Marketable equity securities, realized loss	$ (2,000,000)
Fair value of marketable equity securities	$ 4,700,000	$ 4,700,000	$ 18,100,000
Marketable equity securities, unrealized gain (loss)		1,700,000	$ 12,700,000
Other- than- temporary impairment		$ 0