Other Comprehensive Income - Summary of Tax Effects of Each Component of Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Other Comprehensive Income Loss [Abstract]
Unrealized holding gains (losses) arising during the period, Before-Tax Amount	$ (1,994)	$ (1,056)
Other-than-temporary impairment realized in net income, Before-Tax Amount
Less: reclassification adjustment for (gains) included in net income, Before-Tax Amount	(2,328)	(2,800)
Net unrealized gains (losses), Before-Tax Amount	(4,322)	(3,856)
Change in fair value of derivative instruments designated as cash flow hedges during the period, Before-Tax Amount	2,073	4,951
Less: reclassification adjustment for losses (gains) included in net income, Before-Tax Amount	425	386
Fair value of derivative instruments designated as cash flow hedges, Before-Tax Amount	2,498	5,337
Total other comprehensive income (loss), Before-Tax Amount	(1,824)	1,481
Unrealized holding gains (losses) arising during the period, Tax (Expense) Benefit	698	370
Other-than-temporary impairment realized in net income, Tax (Expense) Benefit
Less: reclassification adjustment for (gains) included in net income, Tax (Expense) Benefit	815	980
Net unrealized gains (losses), Tax (Expense) Benefit	1,513	1,350
Change in fair value of derivative instruments designated as cash flow hedges during the period, Tax (Expense) Benefit	(725)	(1,733)
Less: reclassification adjustment for losses (gains) included in net income, Tax (Expense) Benefit	(149)	(135)
Fair value of derivative instruments designated as cash flow hedges, Tax (Expense) Benefit	(874)	(1,868)
Total other comprehensive income (loss), Tax (Expense) Benefit	639	(518)
Unrealized holding gains (losses) arising during the period, Net-of-Tax Amount	(1,296)	(686)
Other-than-temporary impairment realized in net income, Net-of-Tax Amount
Less: reclassification adjustment for (gains) included in net income, Net-of-Tax Amount	(1,513)	(1,820)
Net unrealized gains (losses), Net-of-Tax Amount	(2,809)	(2,506)
Change in fair value of derivative instruments designated as cash flow hedges during the period, Net-of-Tax Amount	1,348	3,218
Less: reclassification adjustment for losses (gains) included in net income, Net-of-Tax Amount	276	251
Fair value of derivative instruments designated as cash flow hedges, Net-of-Tax Amount	1,624	3,469
Other comprehensive income (loss), net of tax	$ (1,185)	$ 963