Accumulated Other Comprehensive Loss - Comopnents of AOCI (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income (Loss)
Beginning balance	$ 2,377,156
Other comprehensive income before reclassifications	1,547
Amounts reclassified from other comprehensive income	1,460	$ 1,328
Other comprehensive income, net	3,007
Ending balance	2,398,541
Unrealized Gains and Losses on Available for Sale (AFS) Securities
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(10,094)
Other comprehensive income before reclassifications	1,307
Amounts reclassified from other comprehensive income	13
Other comprehensive income, net	1,320
Ending balance	(8,774)
Non-credit Impairment Losses on AFS Securities
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(642)
Other comprehensive income before reclassifications	113
Amounts reclassified from other comprehensive income	(87)
Other comprehensive income, net	26
Ending balance	(616)
Unrealized Gains and (Losses) on Derivatives
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(12,464)
Other comprehensive income before reclassifications	127
Amounts reclassified from other comprehensive income	1,475
Other comprehensive income, net	1,602
Ending balance	(10,862)
Defined Benefit Pension Plan
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(18,893)
Other comprehensive income before reclassifications	0
Amounts reclassified from other comprehensive income	59	$ 43
Other comprehensive income, net	59
Ending balance	(18,834)
Total Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss)
Beginning balance	(42,093)
Ending balance	$ (39,086)