Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financial assets:
Securities available for sale, at fair value	$ 1,293,388	$ 1,290,613
Trust preferred securities
Financial assets:
Securities available for sale, at fair value	8,492	9,986
Recurring
Financial assets:
Securities available for sale, at fair value	1,293,388	1,290,613
Derivative assets:	40,278	8,498
Mortgage loans held for sale in loans held for sale	399,773	318,272
Total financial assets	1,733,439	1,617,383
Financial liabilities:
Derivative instruments	23,081	10,000
Recurring \| Trust preferred securities
Financial assets:
Securities available for sale, at fair value	8,492	9,986
Recurring \| Other available for sale securities
Financial assets:
Securities available for sale, at fair value	1,284,896	1,280,627
Recurring \| Level 1
Financial assets:
Securities available for sale, at fair value	0	0
Derivative assets:	0	0
Mortgage loans held for sale in loans held for sale	0	0
Total financial assets	0	0
Financial liabilities:
Derivative instruments	0	0
Recurring \| Level 1 \| Trust preferred securities
Financial assets:
Securities available for sale, at fair value	0	0
Recurring \| Level 1 \| Other available for sale securities
Financial assets:
Securities available for sale, at fair value	0	0
Recurring \| Level 2
Financial assets:
Securities available for sale, at fair value	1,284,896	1,280,627
Derivative assets:	40,278	8,498
Mortgage loans held for sale in loans held for sale	399,773	318,272
Total financial assets	1,724,947	1,607,397
Financial liabilities:
Derivative instruments	23,081	10,000
Recurring \| Level 2 \| Trust preferred securities
Financial assets:
Securities available for sale, at fair value	0	0
Recurring \| Level 2 \| Other available for sale securities
Financial assets:
Securities available for sale, at fair value	1,284,896	1,280,627
Recurring \| Level 3
Financial assets:
Securities available for sale, at fair value	8,492	9,986
Derivative assets:	0	0
Mortgage loans held for sale in loans held for sale	0	0
Total financial assets	8,492	9,986
Financial liabilities:
Derivative instruments	0	0
Recurring \| Level 3 \| Trust preferred securities
Financial assets:
Securities available for sale, at fair value	8,492	9,986
Recurring \| Level 3 \| Other available for sale securities
Financial assets:
Securities available for sale, at fair value	$ 0	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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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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Fair value portion of mortgage loans held-for-sale.

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