Changes in and Reclassifications from Accumulated Other Comprehensive Income ("AOCI") - Changes in Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance of AOCI - unrealized gains and losses on investment securities AFS			$ 14,132
Unrealized gains and losses on investment securities AFS	$ (10,091)	$ 11,199	(7,600)	$ 22,529
Tax effect of unrealized gains and losses on investment securities AFS	3,844	(4,393)	3,157	(8,837)
Tax effect of amounts reclassified from AOCI	33	7	997	9
Total other comprehensive income (loss)	(6,299)	6,795	(6,064)	13,678
Ending balance of AOCI - unrealized gains and losses on investment securities AFS	8,068	10,006	8,068	10,006
Unrealized gains and losses on investment securities AFS [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance of AOCI - unrealized gains and losses on investment securities AFS	14,367	3,211	14,132	(3,672)
Unrealized gains and losses on investment securities AFS	(10,091)	11,199	(7,600)	22,529
Tax effect of unrealized gains and losses on investment securities AFS	3,844	(4,393)	3,157	(8,837)
Amounts reclassified from AOCI	(84)	(18)	(2,618)	(23)
Tax effect of amounts reclassified from AOCI	32	7	997	9
Total other comprehensive income (loss)	(6,299)	6,795	(6,064)	13,678
Ending balance of AOCI - unrealized gains and losses on investment securities AFS	$ 8,068	$ 10,006	$ 8,068	$ 10,006