Fair Value Measurements Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Available for sale investment securities	$ 2,080,294	$ 2,547,956
Derivative liabilities	47,237	38,997
U.S. Government sponsored agency securities
Available for sale investment securities	31,632
State and municipal securities
Available for sale investment securities	279,095
Corporate debt securities
Available for sale investment securities	109,533
Collateralized mortgage obligations
Available for sale investment securities	832,080
Residential mortgage-backed securities
Available for sale investment securities	463,344
Commercial mortgage-backed securities
Available for sale investment securities	261,616
Auction rate securities
Available for sale investment securities	102,994
Fair Value, Measurements, Recurring
Mortgage loans held for sale	27,099	31,530
Available for sale investment securities	2,080,294	2,547,956
Investments held in Rabbi Trust	18,415	18,982
Derivative assets	62,944	45,008
Total assets	2,188,752	2,643,476
Investments held in Rabbi Trust	18,415	18,982
Derivative liabilities	48,566	39,389
Total liabilities	66,981
Other liabilities		58,371
Fair Value, Measurements, Recurring \| Equity securities
Available for sale investment securities		918
Fair Value, Measurements, Recurring \| U.S. Government sponsored agency securities
Available for sale investment securities	31,632	5,938
Fair Value, Measurements, Recurring \| State and municipal securities
Available for sale investment securities	279,095	408,949
Fair Value, Measurements, Recurring \| Corporate debt securities
Available for sale investment securities	109,533	97,309
Fair Value, Measurements, Recurring \| Collateralized mortgage obligations
Available for sale investment securities	832,080	602,623
Fair Value, Measurements, Recurring \| Residential mortgage-backed securities
Available for sale investment securities	463,344	1,120,796
Fair Value, Measurements, Recurring \| Commercial mortgage-backed securities
Available for sale investment securities	261,616	212,755
Fair Value, Measurements, Recurring \| Auction rate securities
Available for sale investment securities	102,994	98,668
Fair Value, Measurements, Recurring \| Level 1
Mortgage loans held for sale	0	0
Available for sale investment securities	0	918
Investments held in Rabbi Trust	18,415	18,982
Derivative assets	392	469
Total assets	18,807	20,369
Investments held in Rabbi Trust	18,415	18,982
Derivative liabilities	381	375
Total liabilities	18,796
Other liabilities		19,357
Fair Value, Measurements, Recurring \| Level 1 \| Equity securities
Available for sale investment securities		918
Fair Value, Measurements, Recurring \| Level 1 \| U.S. Government sponsored agency securities
Available for sale investment securities	0	0
Fair Value, Measurements, Recurring \| Level 1 \| State and municipal securities
Available for sale investment securities	0	0
Fair Value, Measurements, Recurring \| Level 1 \| Corporate debt securities
Available for sale investment securities	0	0
Fair Value, Measurements, Recurring \| Level 1 \| Collateralized mortgage obligations
Available for sale investment securities	0	0
Fair Value, Measurements, Recurring \| Level 1 \| Residential mortgage-backed securities
Available for sale investment securities	0	0
Fair Value, Measurements, Recurring \| Level 1 \| Commercial mortgage-backed securities
Available for sale investment securities	0	0
Fair Value, Measurements, Recurring \| Level 1 \| Auction rate securities
Available for sale investment securities	0	0
Fair Value, Measurements, Recurring \| Level 2
Mortgage loans held for sale	27,099	31,530
Available for sale investment securities	1,974,025	2,444,613
Investments held in Rabbi Trust	0	0
Derivative assets	62,552	44,539
Total assets	2,063,676	2,520,682
Investments held in Rabbi Trust	0	0
Derivative liabilities	48,185	39,014
Total liabilities	48,185
Other liabilities		39,014
Fair Value, Measurements, Recurring \| Level 2 \| Equity securities
Available for sale investment securities		0
Fair Value, Measurements, Recurring \| Level 2 \| U.S. Government sponsored agency securities
Available for sale investment securities	31,632	5,938
Fair Value, Measurements, Recurring \| Level 2 \| State and municipal securities
Available for sale investment securities	279,095	408,949
Fair Value, Measurements, Recurring \| Level 2 \| Corporate debt securities
Available for sale investment securities	106,258	93,552
Fair Value, Measurements, Recurring \| Level 2 \| Collateralized mortgage obligations
Available for sale investment securities	832,080	602,623
Fair Value, Measurements, Recurring \| Level 2 \| Residential mortgage-backed securities
Available for sale investment securities	463,344	1,120,796
Fair Value, Measurements, Recurring \| Level 2 \| Commercial mortgage-backed securities
Available for sale investment securities	261,616	212,755
Fair Value, Measurements, Recurring \| Level 2 \| Auction rate securities
Available for sale investment securities	0	0
Fair Value, Measurements, Recurring \| Level 3
Mortgage loans held for sale	0	0
Available for sale investment securities	106,269	102,425
Investments held in Rabbi Trust	0	0
Derivative assets	0	0
Total assets	106,269	102,425
Investments held in Rabbi Trust	0	0
Derivative liabilities	0	0
Total liabilities	0
Other liabilities		0
Fair Value, Measurements, Recurring \| Level 3 \| Equity securities
Available for sale investment securities		0
Fair Value, Measurements, Recurring \| Level 3 \| U.S. Government sponsored agency securities
Available for sale investment securities	0	0
Fair Value, Measurements, Recurring \| Level 3 \| State and municipal securities
Available for sale investment securities	0	0
Fair Value, Measurements, Recurring \| Level 3 \| Corporate debt securities
Available for sale investment securities	3,275	3,757
Fair Value, Measurements, Recurring \| Level 3 \| Collateralized mortgage obligations
Available for sale investment securities	0	0
Fair Value, Measurements, Recurring \| Level 3 \| Residential mortgage-backed securities
Available for sale investment securities	0	0
Fair Value, Measurements, Recurring \| Level 3 \| Commercial mortgage-backed securities
Available for sale investment securities	0	0
Fair Value, Measurements, Recurring \| Level 3 \| Auction rate securities
Available for sale investment securities	$ 102,994	$ 98,668

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