Investment Securities - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) Investment	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) Investment	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Amortized Cost and Fair Value Debt Securities [Abstract]
Gross realized gain or loss on sale of Investment Securities	$ 0	$ 0	$ 0	$ 0
Number of investment securities with aggregate gross unrealized losses | Investment	320		320
Unrealized losses on individual investment securities	$ 83,643,000		$ 83,643,000		$ 73,008,000
Cost method investment securities	$ 337,000,000		$ 337,000,000