Investment Securities - Debt Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Investment Securities [Member]
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Available-for-sale Securities, Due within one year, Amortized Cost	$ 767,989
Available-for-sale Securities, Due after one year through five years, Amortized Cost	217,450
Available-for-sale Securities, Due after five years through ten years, Amortized Cost	646,531
Available-for-sale Securities, Due after ten years, Amortized Cost	590,950
Available-for-sale Securities, Amortized Cost Basis	2,222,920	$ 2,216,953
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value [Abstract]
Available-for-sale Securities, Due within one year, Fair Value	767,536
Available-for-sale Securities, Due after one year through five years, Fair Value	217,443
Available-for-sale Securities, Due after five years through ten years, Fair Value	644,361
Available-for-sale Securities, Due after ten years, Fair Value	588,512
Available-for-sale securities	$ 2,217,852	2,215,405
Available-for-sale Securities, Debt Maturities, Weighted Average Yield, Single Maturity Date [Abstract]
Available-for-sale Securities, Due within one year, Weighted-Average Yield	1.29%
Available-for-sale Securities, Due after one year through five years, Weighted-Average Yield	2.76%
Available-for-sale Securities, Due after five years through ten years, Weighted-Average Yield	2.72%
Available-for-sale Securities, Due after ten years, Weighted-Average Yield	2.92%
Available-for-sale Securities, Total Weighted-Average Yield	2.28%
Fixed Interest Rate [Member] \| Government/GSE Guaranteed Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Held-to-maturity, Amortized Cost, before Other-than-temporary Impairment	$ 45,032	45,032
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost [Abstract]
Available-for-sale Securities, Amortized Cost Basis	385	2,589
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value [Abstract]
Available-for-sale securities	403	4,819
Available-for-sale Securities, Debt Maturities, Weighted Average Yield, Single Maturity Date [Abstract]
Debt Securities, Held-to-maturity, Fair Value	$ 45,594	$ 45,564
Held-to-Maturity Securities, Debt Maturities, Weighted-Average Yield	3.50%	2.50%

Available-for-sale Securities, Debt Maturities, after Ten Years, Weighted-Average Yield

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Available-for-sale Securities, Debt Maturities, Next Twelve Months, Weighted-Average Yield

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Available-for-sale Securities, Debt Maturities, Weighted-Average Yield

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Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Weighted-Average Yield

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Available-for-sale Securities, Debt Maturities, Year Two Through Five, Weighted-Average Yield

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Available-for-sale Securities, Debt Maturities, Weighted Average Yield, Single Maturity Date [Abstract]

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Held-to-Maturity Securities, Debt Maturities, Weighted-Average 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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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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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 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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Amortized cost of investment in debt security measured at fair value with change recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in next 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), maturing in next 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 fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before other-than-temporary impairment (OTTI) accretion, of investment in debt securities measured at amortized cost (held-to-maturity).

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

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