Debt Securities Available for Sale - Expected Maturities of Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Amortized Cost
Amortized Cost	$ 1,095,422	$ 1,049,932
Fair Value
Fair Value	1,115,905	1,032,868
Debt Securities excluding Mortgage-based securities and CMOs
Amortized Cost
One year or less	15,098
More than one year to five years	40,046
More than five years to ten years	54,073
More than ten years	5,000
Amortized Cost	114,217
Fair Value
One year or less	15,110
More than one year to five years	40,467
More than five years to ten years	54,483
More than ten years	4,402
Fair Value	114,462
Mortgage-backed securities and collateralized mortgage obligations
Amortized Cost
Amortized Cost	981,205	934,631
Fair Value
Fair Value	$ 1,001,443	$ 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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