Comprehensive Income - Summary of Comprehensive Income Loss (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Amounts Reclassified Out Of Accumulated Other Comprehensive Income Loss [Abstract]
Beginning balance, Gains/(losses) on Cash Flow Hedges			$ (3,733)
Other comprehensive income/(loss) before reclassification, Gains/(losses) on Cash Flow Hedges			922
Amounts reclassified from AOCI, Gains/(losses) on Cash Flow Hedges
Fair Value adjustment on derivatives	19	(146)	922	(414)
Ending balance, Gains/(losses) on Cash Flow Hedges	(2,811)		(2,811)
Beginning balance, Unrealized gains/(losses) on available-for-sale securities			29,464
Other comprehensive income/(loss) before reclassification, Unrealized gains/(losses) on available-for-sale securities	(900)	6,571	(17,057)	9,495
Amounts reclassified from AOCI, Unrealized gains/(losses) on available-for-sale securities	(38)		(347)
Net current period OCI, Unrealized gains/(losses) on available-for-sale securities			(17,404)
Ending Balance, Unrealized gains/(losses) on available-for-sale securities	12,060		12,060
Beginning balance, Defined benefit pension plan items			(628)
Other comprehensive income/(loss) before reclassification, Defined benefit pension plan items
Amounts reclassified from AOCI, Defined benefit pension plan items			71
Net current period OCI, Defined benefit pension plan items			71
Ending balance, Defined benefit pension plan items	(557)		(557)
Beginning balance, Total			25,103
Other comprehensive income/(loss) before reclassification, Total			(16,135)
Amounts reclassified from AOCI, Total			(276)
Net current period OCI, Total	(895)	6,328	(16,411)	8,631
Ending balance, Total	$ 8,692		$ 8,692