Equity - Reclassifications out of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other than temporary impairment		$ 264		$ 377
Realized gains (losses), net	$ 6,316	1,063	$ 10,622	2,155
Total interest expense	23,008	21,151	46,969	40,211
Reclassification out of Accumulated Other Comprehensive Income | Net unrealized gains on available-for-sale securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other than temporary impairment	0	264	0	377
Gain on sale of AFS securities	(5,361)	(718)	(7,050)	(718)
Realized gains (losses), net	(5,361)	(454)	(7,050)	(341)
Reclassification out of Accumulated Other Comprehensive Income | Net unrealized losses on interest rate agreements accounted for as cash flow hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total interest expense	$ 26	$ 39	$ 58	$ 99