Investment Securities - Amortized Cost and Estimated Fair Value of Investments in Debt Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Available-for-sale Securities, Debt Maturities, Amortized Cost [Abstract]
Amortized Cost	$ 1,028,883	$ 1,097,645
Available-for-sale Securities, Debt Maturities, Estimated Fair Value [Abstract]
Estimated Fair Value	1,003,421	1,091,881
Held-to-maturity Securities, Debt Maturities, Amortized Cost [Abstract]
U.S. Government sponsored entities’ asset-backed securities	351,808	357,197
Fair value of securities held-to-maturity	351,422	363,779
Obligations of U.S. Treasury and other U.S. Government sponsored entities
Available-for-sale Securities, Debt Maturities, Amortized Cost [Abstract]
Amortized Cost		245,000
Available-for-sale Securities, Debt Maturities, Estimated Fair Value [Abstract]
Estimated Fair Value		242,720
Obligations of States and Political Subdivisions
Available-for-sale Securities, Debt Maturities, Estimated Fair Value [Abstract]
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Amortized Cost	4,036
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, after Five Through Ten Years, Fair Value	$ 3,987
held to maturity securities weighted avg yield yrs 5-10	3.04%
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, after 10 Years, Amortized Cost	$ 301,242
Debt Securities, Held-to-maturity, Maturity, Allocated and Single Maturity Date, after 10 Years, Fair Value	$ 301,821
Debt Securities, Held-to-maturity, Maturity, after 10 Years, Weighted Average Yield	3.69%
Held-to-maturity Securities, Debt Maturities, Amortized Cost [Abstract]
U.S. Government sponsored entities’ asset-backed securities	$ 305,278	300,412
Fair value of securities held-to-maturity	305,808	306,274
U.S. Government sponsored entity asset-backed securities
Available-for-sale Securities, Debt Maturities, Amortized Cost [Abstract]
Amortized Cost	1,028,883	852,645
Available-for-sale Securities, Debt Maturities, Estimated Fair Value [Abstract]
Estimated Fair Value	$ 1,003,421	849,161
Available for Sale Securities Weighted Avg Yield	2.35%
Held-to-maturity Securities, Debt Maturities, Amortized Cost [Abstract]
U.S. Government sponsored entities’ asset-backed securities	$ 46,530	56,785
Fair value of securities held-to-maturity	$ 45,614	$ 57,505
Held-to-maturity Securities, Debt Maturities, Estimated Fair Value [Abstract]
Held to Maturity Securities weighted avg yield	2.83%

Available for Sale Securities Weighted Avg Yield

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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).

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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Amount of 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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Weighted average yield of investment in debt security measured at amortized cost (held-to-maturity), 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.

+ References

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Weighted average yield of investment in debt security measured at amortized cost (held-to-maturity), 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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Amount of investment in debt security measured at amortized cost (held-to-maturity).

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Amount of investment in debt security measured at amortized cost (held-to-maturity), 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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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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