Investment Securities Gross Unrealized Losses and Fair Values of Investment Securities (Details) $ in Thousands	Mar. 31, 2016 USD ($) securities	Dec. 31, 2015 USD ($)
Available-for-Sale:
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 265,538	$ 556,823
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(812)	(2,667)
Available-for-Sale, 12 Months or More Fair Value	61,120	82,690
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	(376)	(1,058)
Available-for-Sale, Total Fair Value	326,658	639,513
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(1,188)	(3,725)
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months Fair Value	27,229	128,350
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(4,432)	(4,649)
Held-to-Maturity, 12 Months or More Fair Value	27,655	79,015
Held-to-Maturity, 12 Months or More Gross Unrealized Losses	(788)	(1,320)
Held-to-Maturity, Total Fair Value	54,884	207,365
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss1	$ (5,220)	(5,969)
Available-for-Sale and Held-to-Maturity:
Investment Securities in an Unrealized Loss Position (Number of Securities) | securities	109
Obligations of U.S. government agencies
Available-for-Sale:
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 118,698	209,631
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(226)	(1,077)
Available-for-Sale, 12 Months or More Fair Value	35,355	54,619
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	(98)	(533)
Available-for-Sale, Total Fair Value	154,053	264,250
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(324)	(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	146,840	343,875
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(586)	(1,577)
Available-for-Sale, 12 Months or More Fair Value	25,708	28,010
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	(276)	(524)
Available-for-Sale, Total Fair Value	172,548	371,885
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(862)	(2,101)
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months Fair Value	13,801	67,295
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(4,364)	(4,288)
Held-to-Maturity, 12 Months or More Fair Value	24,049	69,539
Held-to-Maturity, 12 Months or More Gross Unrealized Losses	(781)	(1,132)
Held-to-Maturity, Total Fair Value	37,850	136,834
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(5,145)	(5,420)
State, county and municipal securities
Held-to-Maturity:
Held-to-Maturity, Less than 12 Months Fair Value	3,379	10,182
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(7)	(39)
Held-to-Maturity, 12 Months or More Fair Value	3,606	9,476
Held-to-Maturity, 12 Months or More Gross Unrealized Losses	(7)	(188)
Held-to-Maturity, Total Fair Value	6,985	19,658
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(14)	(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	57	61
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	(2)	(1)
Available-for-Sale, Total Fair Value	57	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	10,049	31,135
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	(61)	(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	10,049	31,135
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss1	(61)	(220)
Other Investments
Available-for-Sale:
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0	1,225
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 months, Aggregate Loss1	0	(9)
Available-for-Sale, 12 Months or More Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 months or Longer, Aggregate Loss1	0	0
Available-for-Sale, Total Fair Value	0	1,225
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss1	$ 0	$ (9)