Investment Securities Schedule of Amortized Cost and Fair Values of Investment Securities (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 2,496,457	$ 2,608,210
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments	51,464	46,681
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments	50,145	86,457
Available-for-sale Securities	2,497,776	2,568,434
Equity Securities [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	34,275	33,922
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments	11,987	12,355
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments	14	76
Available-for-sale Securities	46,248	46,201
U.S. Government Securities [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	525	525
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments	0	0
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments	0	0
Available-for-sale Securities	525	525
U.S. Government-Sponsored Agency Securities [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	254	720
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments	6	7
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments	0	1
Available-for-sale Securities	260	726
State and Municipal Securities [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	262,368	281,810
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments	8,244	6,483
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments	789	3,444
Available-for-sale Securities	269,823	284,849
Corporate Debt Securities [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	99,634	100,468
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments	5,881	5,685
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments	4,862	7,404
Available-for-sale Securities	100,653	98,749
Collateralized Mortgage Obligations [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,022,728	1,069,138
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments	8,224	8,036
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments	28,221	44,776
Available-for-sale Securities	1,002,731	1,032,398
Mortgage Backed Securities, Other [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	918,210
Available-for-sale Securities	930,605
Mortgage-Backed Securities [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis		949,328
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments	17,121	13,881
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments	4,726	17,497
Available-for-sale Securities		945,712
Auction Rate Securities [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	158,463	172,299
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments	1	234
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments	11,533	13,259
Available-for-sale Securities	$ 146,931	$ 159,274