Investment Securities Schedule of Amortized Cost and Fair Values of Investment Securities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 2,519,248	$ 2,608,210
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments	46,234	46,681
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments	64,284	86,457
Available-for-sale Securities	2,501,198	2,568,434
Equity Securities [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	34,231	33,922
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments	11,524	12,355
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments	21	76
Available-for-sale Securities	45,734	46,201
U.S. Government Securities [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	526	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	526	525
U.S. Government-Sponsored Agency Securities [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	275	720
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments	6	7
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments	1	1
Available-for-sale Securities	280	726
State and Municipal Securities [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	278,019	281,810
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments	7,190	6,483
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments	1,756	3,444
Available-for-sale Securities	283,453	284,849
Corporate Debt Securities [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	100,348	100,468
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments	6,292	5,685
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments	6,088	7,404
Available-for-sale Securities	100,552	98,749
Collateralized Mortgage Obligations [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,031,968	1,069,138
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments	7,638	8,036
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments	32,869	44,776
Available-for-sale Securities	1,006,737	1,032,398
Mortgage Backed Securities, Other [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	914,502
Available-for-sale Securities	916,203
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	13,582	13,881
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments	11,881	17,497
Available-for-sale Securities		945,712
Auction Rate Securities [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	159,379	172,299
Available-for-sale Securities, Gross Unrealized Gain, Accumulated Investments	2	234
Available-for-sale Securities, Gross Unrealized Loss, Accumulated Investments	11,668	13,259
Available-for-sale Securities	$ 147,713	$ 159,274