Debt Securities Available for Sale - Expected Maturities of Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Amortized Cost
Amortized Cost	$ 1,079,469	$ 1,086,143
Fair Value
Fair Value	1,116,417	1,098,336
Debt Securities excluding Mortgage-based securities and CMOs
Amortized Cost
One year or less	31,476
More than one year to five years	25,971
More than five years to ten years	52,572
More than ten years	5,473
Amortized Cost	115,492
Fair Value
One year or less	31,584
More than one year to five years	26,773
More than five years to ten years	51,555
More than ten years	4,467
Fair Value	114,379
Mortgage-backed securities and collateralized mortgage obligations
Amortized Cost
Amortized Cost	963,977	968,165
Fair Value
Fair Value	$ 1,002,038	$ 979,881

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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