Other Comprehensive Income (Loss) - Summary of Reclassification Out of Each Component of Accumulated Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Mar. 31, 2014	Jun. 30, 2015	Jun. 30, 2014
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Net gains on securities available for sale		$ 31		$ 11	$ 34
Tax expense	$ (2,040)	38,837		(3,855)	38,681
Net income	$ 4,125	42,404	$ 42,404	7,811	44,498
Amount Reclassified From Accumulated Other Comprehensive Income [Member] | Realized Net Gains on Sale of Available for Sale Securities [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income On Derivatives [Line Items]
Net gains on securities available for sale		(31)		(11)	(34)
Tax expense		11		4	12
Net income		$ (20)		$ (7)	$ (22)