Investment Securities Gross Unrealized Losses and Fair Values of Investment Securities (Details) $ in Thousands	Dec. 31, 2015 USD ($) securities	Dec. 31, 2014 USD ($) securities
Available-for-Sale:
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 556,823	$ 355,102
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(2,667)	(1,589)
Available-for-Sale, 12 months or more fair value	82,690	460,753
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,058)	(7,407)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	639,513	815,855
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(3,725)	(8,996)
Held-to-Maturity:
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	128,350	83,935
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(4,649)	(1,846)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	79,015	20,097
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,320)	(373)
Held-to-maturity Securities, Fair Value	207,365	104,032
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (5,969)	$ (2,219)
Available-for-Sale and Held-to-Maturity:
Investment securities in an unrealized loss position (number of securities) | securities	198	154
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, Accumulated Loss	(4)
Available-for-Sale, 12 months or more fair value	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	2,092
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(4)
State, county and municipal securities
Held-to-Maturity:
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	10,182	$ 7,979
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(39)	(13)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	9,476	20,097
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(188)	(373)
Held-to-maturity Securities, Fair Value	19,658	28,076
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	(227)	(386)
Obligations of U.S. government agencies
Available-for-Sale:
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	209,631	135,888
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1,077)	(702)
Available-for-Sale, 12 months or more fair value	54,619	309,283
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(533)	(4,668)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	264,250	445,171
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(1,610)	(5,370)
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	343,875	219,214
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1,577)	(887)
Available-for-Sale, 12 months or more fair value	28,010	151,380
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(524)	(2,737)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	371,885	370,594
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(2,101)	(3,624)
Held-to-Maturity:
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	87,033	61,201
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(4,390)	(1,758)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	69,539	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1,132)	0
Held-to-maturity Securities, Fair Value	156,572	61,201
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	(5,522)	(1,758)
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, Accumulated Loss	0	0
Available-for-Sale, 12 months or more fair value	61	90
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(1)	(2)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	61	90
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(1)	(2)
Corporate securities
Held-to-Maturity:
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	31,135	14,755
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(220)	(75)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Held-to-maturity Securities, Fair Value	31,135	14,755
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	(220)	$ (75)
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, Accumulated Loss	(9)
Available-for-Sale, 12 months or more fair value	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,225
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (9)