Fair Value Measurements Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Securities available for sale	$ 2,559,227	$ 2,484,773
Equity securities
Securities available for sale	24,526	21,514
U.S. Government sponsored agency securities
Securities available for sale	134	25,136
State and municipal securities
Securities available for sale	391,641	262,765
Corporate debt securities
Securities available for sale	109,409	96,955
Collateralized mortgage obligations
Securities available for sale	593,860	821,509
Mortgage-backed securities
Securities available for sale	1,342,401	1,158,835
Auction rate securities
Securities available for sale	97,256	98,059
Fair Value, Measurements, Recurring
Mortgage loans held for sale	28,697	16,886
Securities available for sale	2,559,227	2,484,773
Other financial assets	61,592	50,594
Total assets	2,649,516	2,552,253
Other financial liabilities	58,766	48,924
Fair Value, Measurements, Recurring | Equity securities
Securities available for sale	24,526	21,514
Fair Value, Measurements, Recurring | U.S. Government sponsored agency securities
Securities available for sale	134	25,136
Fair Value, Measurements, Recurring | State and municipal securities
Securities available for sale	391,641	262,765
Fair Value, Measurements, Recurring | Corporate debt securities
Securities available for sale	109,409	96,955
Fair Value, Measurements, Recurring | Collateralized mortgage obligations
Securities available for sale	593,860	821,509
Fair Value, Measurements, Recurring | Mortgage-backed securities
Securities available for sale	1,342,401	1,158,835
Fair Value, Measurements, Recurring | Auction rate securities
Securities available for sale	97,256	98,059
Fair Value, Measurements, Recurring | Level 1
Mortgage loans held for sale	0	0
Securities available for sale	24,526	21,514
Other financial assets	17,111	16,129
Total assets	41,637	37,643
Other financial liabilities	17,032	15,914
Fair Value, Measurements, Recurring | Level 1 | Equity securities
Securities available for sale	24,526	21,514
Fair Value, Measurements, Recurring | Level 1 | U.S. Government sponsored agency securities
Securities available for sale	0	0
Fair Value, Measurements, Recurring | Level 1 | State and municipal securities
Securities available for sale	0	0
Fair Value, Measurements, Recurring | Level 1 | Corporate debt securities
Securities available for sale	0	0
Fair Value, Measurements, Recurring | Level 1 | Collateralized mortgage obligations
Securities available for sale	0	0
Fair Value, Measurements, Recurring | Level 1 | Mortgage-backed securities
Securities available for sale	0	0
Fair Value, Measurements, Recurring | Level 1 | Auction rate securities
Securities available for sale	0	0
Fair Value, Measurements, Recurring | Level 2
Mortgage loans held for sale	28,697	16,886
Securities available for sale	2,434,573	2,361,864
Other financial assets	44,481	34,465
Total assets	2,507,751	2,413,215
Other financial liabilities	41,734	33,010
Fair Value, Measurements, Recurring | Level 2 | Equity securities
Securities available for sale	0	0
Fair Value, Measurements, Recurring | Level 2 | U.S. Government sponsored agency securities
Securities available for sale	134	25,136
Fair Value, Measurements, Recurring | Level 2 | State and municipal securities
Securities available for sale	391,641	262,765
Fair Value, Measurements, Recurring | Level 2 | Corporate debt securities
Securities available for sale	106,537	93,619
Fair Value, Measurements, Recurring | Level 2 | Collateralized mortgage obligations
Securities available for sale	593,860	821,509
Fair Value, Measurements, Recurring | Level 2 | Mortgage-backed securities
Securities available for sale	1,342,401	1,158,835
Fair Value, Measurements, Recurring | Level 2 | Auction rate securities
Securities available for sale	0	0
Fair Value, Measurements, Recurring | Level 3
Mortgage loans held for sale	0	0
Securities available for sale	100,128	101,395
Other financial assets	0	0
Total assets	100,128	101,395
Other financial liabilities	0	0
Fair Value, Measurements, Recurring | Level 3 | Equity securities
Securities available for sale	0	0
Fair Value, Measurements, Recurring | Level 3 | U.S. Government sponsored agency securities
Securities available for sale	0	0
Fair Value, Measurements, Recurring | Level 3 | State and municipal securities
Securities available for sale	0	0
Fair Value, Measurements, Recurring | Level 3 | Corporate debt securities
Securities available for sale	2,872	3,336
Fair Value, Measurements, Recurring | Level 3 | Collateralized mortgage obligations
Securities available for sale	0	0
Fair Value, Measurements, Recurring | Level 3 | Mortgage-backed securities
Securities available for sale	0	0
Fair Value, Measurements, Recurring | Level 3 | Auction rate securities
Securities available for sale	$ 97,256	$ 98,059