Securities Available for Sale - Amortized Cost and Estimated Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost - Due within one year	$ 80
Amortized Cost - Due after one year through five years	349
Amortized Cost - Due after five years through ten years	0
Amortized Cost - Due after ten years	74,202
Amortized Cost	1,703,841	$ 1,893,618
Estimated Fair Value - Due within one year	80
Estimated Fair Value - Due after one year through five years	351
Estimated Fair Value - Due after five years through ten years	0
Estimated Fair Value - Due after ten years	73,880
Estimated Fair Value	1,715,987	1,846,265
Carrying values of securities pledged as collateral	340,900	354,600
Collateralized Mortgage Obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	735,094
Amortized Cost	735,094	914,710
Estimated Fair Value	736,655
Estimated Fair Value	736,655	895,122
Mortgage-backed Securities, Residential
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	353,073
Amortized Cost	353,073	415,659
Estimated Fair Value	352,897
Estimated Fair Value	352,897	402,605
Mortgage-backed Securities, Commercial
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	541,043
Amortized Cost	541,043	481,081
Estimated Fair Value	552,124
Estimated Fair Value	552,124	469,126
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5,000	5,000
Estimated Fair Value	$ 4,200	$ 3,826

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

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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.

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in sixth fiscal year through tenth fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in sixth through tenth fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in second through fifth fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in second through fifth fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing after tenth fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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Amount of restricted investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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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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