Accumulated Other Comprehensive Loss - Schedule of Changes in Accumulated Other Comprehensive Loss After Tax (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Accumulated Other Comprehensive Income (Loss)
Beginning balance			$ 2,207,091
Other comprehensive income (loss) before reclassifications	$ (2,456)		(784)
Amounts reclassified from other comprehensive income (loss)	2,152	$ 1,147	3,480	$ 724
Total other comprehensive income (loss)	(304)		2,696
Ending balance	2,232,212		2,232,212
Unrealized Gains and Losses on Available for Sale (AFS) Securities
Accumulated Other Comprehensive Income (Loss)
Beginning balance	2,777		(5,336)
Other comprehensive income (loss) before reclassifications	(635)		7,648
Amounts reclassified from other comprehensive income (loss)	2		(168)
Total other comprehensive income (loss)	(633)		7,480
Ending balance	2,144		2,144
Non-credit Impairment Losses on AFS Securities
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(865)		(520)
Other comprehensive income (loss) before reclassifications	301		242
Amounts reclassified from other comprehensive income (loss)	0		(286)
Total other comprehensive income (loss)	301		(44)
Ending balance	(564)		(564)
Unrealized Gains and (Losses) on Derivatives
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(22,455)		(17,644)
Other comprehensive income (loss) before reclassifications	(2,122)		(8,674)
Amounts reclassified from other comprehensive income (loss)	2,107		3,848
Total other comprehensive income (loss)	(15)		(4,826)
Ending balance	(22,470)		(22,470)
Total Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(42,695)		(45,695)
Ending balance	(42,999)		(42,999)
Defined Benefit Pension Plan
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(22,152)		(22,195)
Other comprehensive income (loss) before reclassifications	0		0
Amounts reclassified from other comprehensive income (loss)	43	$ 121	86	$ 240
Total other comprehensive income (loss)	43		86
Ending balance	$ (22,109)		$ (22,109)