Available-For-Sale Securities - Additional Information (Detail)	3 Months Ended	6 Months Ended	12 Months Ended
	Mar. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($) Investment
Investments Debt And Equity Securities [Abstract]
Number of investments in marketable equity securities | Investment			1
Marketable equity securities, realized gain	$ 3,300,000
Fair value of marketable equity securities			$ 4,100,000
Marketable equity securities, unrealized gain (loss)			$ 2,300,000
Other- than- temporary impairment		$ 0