Fair Value Measurements on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financial Assets
Debt securities, available-for-sale	$ 2,103,619	$ 1,778,243
Recurring Measurements
Financial Assets
Loans held for sale, at fair value	50,649	38,833
Total assets measured at fair value on a recurring basis	2,154,268	1,817,076
Financial Liabilities
Total liabilities measured at fair value on a recurring basis	142	9,389
Interest Rate Swaps \| Recurring Measurements
Financial Liabilities
Derivatives	142	9,389
U.S. government and federal agency \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	25,267	31,127
U.S. government sponsored enterprises \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	118,550	19,091
State and local governments \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	644,014	629,501
Corporate bonds \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	305,225	216,762
Residential mortgage-backed securities \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	826,164	779,283
Commercial mortgage-backed securities \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	184,399	102,479
Level 1 \| Recurring Measurements
Financial Assets
Loans held for sale, at fair value	0	0
Total assets measured at fair value on a recurring basis	0	0
Financial Liabilities
Total liabilities measured at fair value on a recurring basis	0	0
Level 1 \| Interest Rate Swaps \| Recurring Measurements
Financial Liabilities
Derivatives	0	0
Level 1 \| U.S. government and federal agency \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	0	0
Level 1 \| U.S. government sponsored enterprises \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	0	0
Level 1 \| State and local governments \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	0	0
Level 1 \| Corporate bonds \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	0	0
Level 1 \| Residential mortgage-backed securities \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	0	0
Level 1 \| Commercial mortgage-backed securities \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	0	0
Level 2 \| Recurring Measurements
Financial Assets
Loans held for sale, at fair value	50,649	38,833
Total assets measured at fair value on a recurring basis	2,154,268	1,817,076
Financial Liabilities
Total liabilities measured at fair value on a recurring basis	142	9,389
Level 2 \| Interest Rate Swaps \| Recurring Measurements
Financial Liabilities
Derivatives	142	9,389
Level 2 \| U.S. government and federal agency \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	25,267	31,127
Level 2 \| U.S. government sponsored enterprises \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	118,550	19,091
Level 2 \| State and local governments \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	644,014	629,501
Level 2 \| Corporate bonds \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	305,225	216,762
Level 2 \| Residential mortgage-backed securities \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	826,164	779,283
Level 2 \| Commercial mortgage-backed securities \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	184,399	102,479
Level 3 \| Recurring Measurements
Financial Assets
Loans held for sale, at fair value	0	0
Total assets measured at fair value on a recurring basis	0	0
Financial Liabilities
Total liabilities measured at fair value on a recurring basis	0	0
Level 3 \| Interest Rate Swaps \| Recurring Measurements
Financial Liabilities
Derivatives	0	0
Level 3 \| U.S. government and federal agency \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	0	0
Level 3 \| U.S. government sponsored enterprises \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	0	0
Level 3 \| State and local governments \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	0	0
Level 3 \| Corporate bonds \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	0	0
Level 3 \| Residential mortgage-backed securities \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	0	0
Level 3 \| Commercial mortgage-backed securities \| Recurring Measurements
Financial Assets
Debt securities, available-for-sale	$ 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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Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

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