Premises and Equipment - Components and Depreciation and Amortization Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Components of premises and equipment
Premises and equipment	$ 566,822	$ 547,071
Less: Accumulated depreciation and amortization	244,421	230,186
Net book value	322,401	316,885
Depreciation and amortization expenses	15,952	14,522	$ 15,303
Occupancy
Components of premises and equipment
Depreciation and amortization expenses	9,231	9,037	8,815
Equipment
Components of premises and equipment
Depreciation and amortization expenses	6,721	5,485	$ 6,488
Buildings
Components of premises and equipment
Premises and equipment	296,107	289,271
Furniture and equipment
Components of premises and equipment
Premises and equipment	98,800	86,485
Land
Components of premises and equipment
Premises and equipment	114,852	106,487
Leasehold improvements
Components of premises and equipment
Premises and equipment	$ 57,063	$ 64,828

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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