Accumulated Other Comprehensive Income (Loss) - Schedule of AOCI (Detail) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended
Jan. 02, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance				$ 2,154,397	$ 1,814,417
Other comprehensive income (loss) before reclassifications		$ (13,441)	$ (2,397)	(18,826)	25,942
Amounts reclassified from AOCI to income		214	(680)	(29)	(767)
Amount reclassified from AOCI to retained earnings for cumulative effect of change in accounting principle		(4,179)		(4,179)
Amounts reclassified from AOCI to retained earnings related to the Tax Cuts and Jobs Act of 2017	$ 10,800
Ending Balance		2,220,680	1,906,823	2,220,680	1,906,823
Gains and Losses on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		2,277	(5,645)	(2,337)	(6,715)
Other comprehensive income (loss) before reclassifications		548	134	5,135	(986)
Amounts reclassified from AOCI to income		(171)	887	417	3,077
Amount reclassified from AOCI to retained earnings for cumulative effect of change in accounting principle		(52)		(52)
Amounts reclassified from AOCI to retained earnings related to the Tax Cuts and Jobs Act of 2017				(509)
Ending Balance		2,654	(4,624)	2,654	(4,624)
Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(59,356)	(12,457)	(35,557)	(39,012)
Other comprehensive income (loss) before reclassifications		(13,989)	(2,531)	(28,475)	26,928
Amounts reclassified from AOCI to income		(117)	(1,883)	(1,847)	(4,787)
Amounts reclassified from AOCI to retained earnings related to the Tax Cuts and Jobs Act of 2017				(7,583)
Ending Balance		(73,462)	(16,871)	(73,462)	(16,871)
Accumulated Unrealized Gains and Losses on Held-to-Maturity Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(9,335)	(12,717)	(12,107)	(13,310)
Other comprehensive income (loss) before reclassifications				4,514
Amounts reclassified from AOCI to income		482	300	1,340	893
Amounts reclassified from AOCI to retained earnings related to the Tax Cuts and Jobs Act of 2017				(2,600)
Ending Balance		(8,853)	(12,417)	(8,853)	(12,417)
Defined Benefit Pension Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(289)	(301)	(271)	(335)
Amounts reclassified from AOCI to income		20	16	61	50
Amounts reclassified from AOCI to retained earnings related to the Tax Cuts and Jobs Act of 2017				(59)
Ending Balance		(269)	(285)	(269)	(285)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(66,703)	(31,120)	(50,272)	(59,372)
Amount reclassified from AOCI to retained earnings for cumulative effect of change in accounting principle		(52)		(52)
Amounts reclassified from AOCI to retained earnings related to the Tax Cuts and Jobs Act of 2017				(10,751)
Ending Balance		$ (79,930)	$ (34,197)	$ (79,930)	$ (34,197)

Tax Cuts and Jobs Act of 2017, reclassification from AOCI to retained earnings tax effect.

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Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

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Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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Amount after tax of reclassification adjustments of other comprehensive income (loss).

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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