Portion of Net Unrealized Losses Recognized to Equity Securities (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Gain (Loss) on Investments [Line Items]
Net Unrealized Losses recognized during the reporting period	$ (3,181)
Equity Securities
Gain (Loss) on Investments [Line Items]
Total Net Realized and Unrealized Losses recognized during the period	(3,396)
Less: Net Realized Losses on Investments Sold recognized during the period	(215)
Net Unrealized Losses recognized during the reporting period	$ (3,181)