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

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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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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Accumulated Other Comprehensive Income (Loss) - Schedule of AOCI (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 2,689,570	$ 2,154,397
Amount reclassified from AOCI to retainedearnings for cumulative effect ofchange in accounting principle			$ 6,322	$ (4,179)
Amounts reclassified from AOCI to retainedearnings related to the Tax Cuts and JobsAct of 2017		0
Ending Balance	2,751,872	2,179,118
Gains and Losses on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	1,099	(2,337)
Amount reclassified from AOCI to retainedearnings for cumulative effect ofchange in accounting principle		(52)
Amounts reclassified from AOCI to retainedearnings related to the Tax Cuts and JobsAct of 2017		(509)
Other comprehensive income (loss) before reclassifications	(296)	3,444
Amounts reclassified from AOCI to income	(290)	580
Ending Balance	513	1,126
Unrealized Gains and Losses on Available- for-Sale Debt Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(37,348)	(35,557)
Amount reclassified from AOCI to retainedearnings for cumulative effect ofchange in accounting principle		0
Amounts reclassified from AOCI to retainedearnings related to the Tax Cuts and JobsAct of 2017		(7,583)
Other comprehensive income (loss) before reclassifications	47,711	(8,872)
Amounts reclassified from AOCI to income	79	(593)
Ending Balance	10,442	(52,605)
Accumulated Unrealized Gains and Losses on Held-to-Maturity Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(8,515)	(12,107)
Amount reclassified from AOCI to retainedearnings for cumulative effect ofchange in accounting principle		0
Amounts reclassified from AOCI to retainedearnings related to the Tax Cuts and JobsAct of 2017		(2,600)
Other comprehensive income (loss) before reclassifications	0	4,514
Amounts reclassified from AOCI to income	351	456
Ending Balance	(8,164)	(9,737)
Defined Benefit Pension Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(186)	(271)
Amount reclassified from AOCI to retainedearnings for cumulative effect ofchange in accounting principle		0
Amounts reclassified from AOCI to retainedearnings related to the Tax Cuts and JobsAct of 2017		(59)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from AOCI to income	15	20
Ending Balance	(171)	(310)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(44,950)	(50,272)
Amount reclassified from AOCI to retainedearnings for cumulative effect ofchange in accounting principle		(52)	$ 0	$ (52)
Amounts reclassified from AOCI to retainedearnings related to the Tax Cuts and JobsAct of 2017		(10,751)
Other comprehensive income (loss) before reclassifications	47,415	(914)
Amounts reclassified from AOCI to income	155	463
Ending Balance	$ 2,620	$ (61,526)