Investment Securities Gross Unrealized Losses and Fair Values of Investment Securities (Details) $ in Thousands	Jun. 30, 2016 USD ($) securities	Dec. 31, 2015 USD ($) securities
Available-for-Sale:
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 11,097	$ 556,823
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(41)	(2,667)
Available-for-Sale, 12 Months or More Fair Value	29,140	82,690
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	(99)	(1,058)
Available-for-Sale, Total Fair Value	40,237	639,513
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(140)	(3,725)
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months Fair Value	5,655	128,350
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(2,631)	(4,649)
Held-to-Maturity, 12 Months or More Fair Value	22,916	79,015
Held-to-Maturity, 12 Months or More Gross Unrealized Losses	(3,147)	(1,320)
Held-to-Maturity, Total Fair Value	28,571	207,365
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss1	$ (5,778)	$ (5,969)
Available-for-Sale and Held-to-Maturity:
Investment Securities in an Unrealized Loss Position (Number of Securities) | securities	55	198
US Treasury Securities [Member]
Available-for-Sale:
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		$ 2,092
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1		(4)
Available-for-Sale, 12 Months or More Fair Value		0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1		0
Available-for-Sale, Total Fair Value		2,092
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1		(4)
Obligations of U.S. government agencies
Available-for-Sale:
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 0	209,631
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	0	(1,077)
Available-for-Sale, 12 Months or More Fair Value	10,477	54,619
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	(21)	(533)
Available-for-Sale, Total Fair Value	10,477	264,250
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(21)	(1,610)
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months Fair Value		19,738
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1		(102)
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		19,738
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss1		(102)
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	11,097	343,875
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(41)	(1,577)
Available-for-Sale, 12 Months or More Fair Value	18,609	28,010
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	(76)	(524)
Available-for-Sale, Total Fair Value	29,706	371,885
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(117)	(2,101)
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months Fair Value	5,030	67,295
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(2,631)	(4,288)
Held-to-Maturity, 12 Months or More Fair Value	20,683	69,539
Held-to-Maturity, 12 Months or More Gross Unrealized Losses	(3,146)	(1,132)
Held-to-Maturity, Total Fair Value	25,713	136,834
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(5,777)	(5,420)
State, county and municipal securities
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months Fair Value	625	10,182
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	0	(39)
Held-to-Maturity, 12 Months or More Fair Value	2,233	9,476
Held-to-Maturity, 12 Months or More Gross Unrealized Losses	(1)	(188)
Held-to-Maturity, Total Fair Value	2,858	19,658
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(1)	(227)
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	54	61
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	(2)	(1)
Available-for-Sale, Total Fair Value	54	61
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1	$ (2)	(1)
Corporate securities
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months Fair Value		31,135
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1		(220)
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		31,135
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss1		(220)
Other Investments
Available-for-Sale:
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value		1,225
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1		(9)
Available-for-Sale, 12 Months or More Fair Value		0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1		0
Available-for-Sale, Total Fair Value		1,225
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1		$ (9)