Securities (Amortized Cost and Fair Value of Securities Available for Sale) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	$ 4,709,075	$ 4,637,610	$ 4,637,610
Securities Available for Sale, Gross Unrealized Gains	185,281		52,367
Securities Available for Sale, Gross Unrealized Losses	360		14,673
Securities Available for Sale, Fair Value	4,893,996	$ 4,675,304	4,675,304
U.S. Treasury And Government Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	107,750		98,320
Securities Available for Sale, Gross Unrealized Gains	1,676		652
Securities Available for Sale, Gross Unrealized Losses	223		300
Securities Available for Sale, Fair Value	109,203		98,672
Municipal Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	241,050		242,016
Securities Available for Sale, Gross Unrealized Gains	8,643		7,789
Securities Available for Sale, Fair Value	249,693		249,805
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	2,061,777		1,910,909
Securities Available for Sale, Gross Unrealized Gains	62,764		20,268
Securities Available for Sale, Gross Unrealized Losses	10		7,020
Securities Available for Sale, Fair Value	2,124,531		1,924,157
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	1,648,643		1,570,765
Securities Available for Sale, Gross Unrealized Gains	94,268		19,880
Securities Available for Sale, Gross Unrealized Losses	105		4,178
Securities Available for Sale, Fair Value	1,742,806		1,586,467
Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	641,855		807,600
Securities Available for Sale, Gross Unrealized Gains	17,712		3,757
Securities Available for Sale, Gross Unrealized Losses			3,142
Securities Available for Sale, Fair Value	659,567		808,215
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities Available for Sale, Gross Amortized Cost	8,000		8,000
Securities Available for Sale, Gross Unrealized Gains	218		21
Securities Available for Sale, Gross Unrealized Losses	22		33
Securities Available for Sale, Fair Value	$ 8,196		$ 7,988

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

No definition available.

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- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

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- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

No definition available.

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- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

No definition available.

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- Definition

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.

+ References

No definition available.

+ Details

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