Debt Securities Available for Sale - Expected Maturities of Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Amortized Cost
Securities available-for-sale, amortized cost	$ 1,086,143	$ 1,049,932
Fair Value
Securities available for sale, at fair value	1,098,336	1,032,868
Debt Securities Excluding Mortgage-Based Securities
Amortized Cost
One year or less	31,901
More than one year to five years	27,366
More than five years to ten years	53,235
More than ten years	5,476
Securities available-for-sale, amortized cost	117,978
Fair Value
One year or less	31,955
More than one year to five years	27,729
More than five years to ten years	53,669
More than ten years	5,102
Securities available for sale, at fair value	118,455
Mortgage-backed securities and collateralized mortgage obligations
Amortized Cost
Securities available-for-sale, amortized cost	968,165	934,631
Fair Value
Securities available for sale, at fair value	$ 979,881	$ 920,007

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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