Investment Securities - Additional Information (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($) Investment	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) Investment	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Amortized Cost and Fair Value Debt Securities [Abstract]
Gross realized gains on sale of investment securities	$ 0	$ 0	$ 0	$ 0
Number of investment securities with aggregate gross unrealized losses | Investment	428		428
Unrealized losses on individual investment securities	$ 66,863,000		$ 66,863,000		$ 120,269,000
Cost method investment securities	$ 470,000,000		$ 470,000,000