Investment Securities Gross Unrealized Losses and Fair Values of Investment Securities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014 securities	Dec. 31, 2013 securities
Available-for-Sale:
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 717,567	$ 1,092,584
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(11,130)	(27,628)
Available-for-Sale, 12 Months or More Fair Value	449,032	226,396
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	(13,517)	(9,769)
Available-for-Sale, Total Fair Value	1,166,599	1,318,980
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(24,647)	(37,397)
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months Fair Value	21,088	44,844
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(473)	(1,327)
Held-to-Maturity, 12 Months or More Fair Value	21,777	14,296
Held-to-Maturity, 12 Months or More Gross Unrealized Losses	(736)	(730)
Held-to-Maturity, Total Fair Value	42,865	59,140
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(1,209)	(2,057)
Available-for-Sale and Held-to-Maturity:
Investment Securities in an Unrealized Loss Position (Number of Securities)	198	229
Obligations of U.S. government agencies
Available-for-Sale:
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	289,936	458,385
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(4,862)	(10,355)
Available-for-Sale, 12 Months or More Fair Value	143,933	59,362
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	(3,004)	(1,894)
Available-for-Sale, Total Fair Value	433,869	517,747
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(7,866)	(12,249)
U.S. agency residential mortgage-backed securities & collateralized mortgage obligations
Available-for-Sale:
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	427,631	634,199
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(6,268)	(17,273)
Available-for-Sale, 12 Months or More Fair Value	304,999	166,930
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	(10,511)	(7,874)
Available-for-Sale, Total Fair Value	732,630	801,129
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(16,779)	(25,147)
Private mortgage-backed securities
Available-for-Sale:
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	0	0
Available-for-Sale, 12 Months or More Fair Value	100	104
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	(2)	(1)
Available-for-Sale, Total Fair Value	100	104
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(2)	(1)
State, county and municipal securities
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months Fair Value	21,088	37,550
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(473)	(1,319)
Held-to-Maturity, 12 Months or More Fair Value	21,777	14,296
Held-to-Maturity, 12 Months or More Gross Unrealized Losses	(736)	(730)
Held-to-Maturity, Total Fair Value	42,865	51,846
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(1,209)	(2,049)
Corporate Debt Securities [Member]
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months Fair Value		7,294
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1		(8)
Held-to-Maturity, 12 Months or More Fair Value		0
Held-to-Maturity, 12 Months or More Gross Unrealized Losses		0
Held-to-Maturity, Total Fair Value		7,294
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss1		$ (8)