Investment Securities Gross Unrealized Losses and Fair Values of Investment Securities (Details) $ in Thousands	Sep. 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	$ 83,050	$ 556,823
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(222)	(2,667)
Available-for-Sale, 12 Months or More Fair Value	121,245	82,690
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	(320)	(1,058)
Available-for-Sale, Total Fair Value	204,295	639,513
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(542)	(3,725)
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months Fair Value	21,593	128,350
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(2,759)	(4,649)
Held-to-Maturity, 12 Months or More Fair Value	21,366	79,015
Held-to-Maturity, 12 Months or More Gross Unrealized Losses	(3,866)	(1,320)
Held-to-Maturity, Total Fair Value	42,959	207,365
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss1	$ (6,625)	$ (5,969)
Available-for-Sale and Held-to-Maturity:
Investment Securities in an Unrealized Loss Position (Number of Securities) | securities	126	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	103,776	54,619
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	(180)	(533)
Available-for-Sale, Total Fair Value	103,776	264,250
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(180)	(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	83,050	343,875
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(222)	(1,577)
Available-for-Sale, 12 Months or More Fair Value	17,419	28,010
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	(139)	(524)
Available-for-Sale, Total Fair Value	100,469	371,885
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(361)	(2,101)
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months Fair Value	8,791	67,295
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(2,721)	(4,288)
Held-to-Maturity, 12 Months or More Fair Value	18,523	69,539
Held-to-Maturity, 12 Months or More Gross Unrealized Losses	(3,860)	(1,132)
Held-to-Maturity, Total Fair Value	27,314	136,834
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(6,581)	(5,420)
State, county and municipal securities
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months Fair Value	7,746	10,182
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(24)	(39)
Held-to-Maturity, 12 Months or More Fair Value	2,843	9,476
Held-to-Maturity, 12 Months or More Gross Unrealized Losses	(6)	(188)
Held-to-Maturity, Total Fair Value	10,589	19,658
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(30)	(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	50	61
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	(1)	(1)
Available-for-Sale, Total Fair Value	50	61
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(1)	(1)
Corporate securities
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months Fair Value	5,056	31,135
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(14)	(220)
Held-to-Maturity, 12 Months or More Fair Value	0	0
Held-to-Maturity, 12 Months or More Gross Unrealized Losses	0	0
Held-to-Maturity, Total Fair Value	5,056	31,135
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss1	$ (14)	(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)