Securities Available for Sale - Roll-Forward of Credit Loss Component of Other-than-Temporary Impairment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Beginning credit loss amount	$ 0	$ 1,674	$ 1,240
Add: Initial OTTI credit losses	0	0	0
Subsequent OTTI credit losses	0	0	434
Less: Realized losses for securities sold	0	1,674	0
Securities intended or required to be sold	0	0	0
Increases in expected cash flows on debt securities	0	0	0
Ending credit loss amount	$ 0	$ 0	$ 1,674