Investment Securities (Available-for-sale Securities with Unrealized Loss) (Details) $ in Thousands	Sep. 30, 2018 USD ($) securities	Dec. 31, 2017 USD ($) securities
Available-for-sale securities that had an unrealized loss:
Less than 12 months, fair value	$ 257,288	$ 294,746
Less than 12 months, unrealized loss	$ 5,771	$ 3,575
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities	166	97
12 months or more, fair value	$ 420,029	$ 301,298
12 months or more, unrealized loss	$ 22,610	$ 10,010
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | securities	138	94
Total unrealized loss position, fair value	$ 677,317	$ 596,044
Total unrealized loss	28,381	13,585
States and political subdivisions
Available-for-sale securities that had an unrealized loss:
Less than 12 months, fair value	30,112	16,985
Less than 12 months, unrealized loss	$ 224	$ 89
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities	52	18
12 months or more, fair value	$ 9,480	$ 5,308
12 months or more, unrealized loss	$ 585	$ 167
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | securities	6	1
Total unrealized loss position, fair value	$ 39,592	$ 22,293
Total unrealized loss	809	256
Residential mortgage-backed securities
Available-for-sale securities that had an unrealized loss:
Less than 12 months, fair value	224,049	274,998
Less than 12 months, unrealized loss	$ 5,503	$ 3,462
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities	113	77
12 months or more, fair value	$ 405,124	$ 291,812
12 months or more, unrealized loss	$ 21,759	$ 9,556
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | securities	128	88
Total unrealized loss position, fair value	$ 629,173	$ 566,810
Total unrealized loss	27,262	13,018
Commercial mortgage-backed securities
Available-for-sale securities that had an unrealized loss:
Less than 12 months, fair value	3,127	2,487
Less than 12 months, unrealized loss	$ 44	$ 23
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities	1	1
12 months or more, fair value	$ 3,587	$ 1,274
12 months or more, unrealized loss	$ 104	$ 16
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | securities	2	1
Total unrealized loss position, fair value	$ 6,714	$ 3,761
Total unrealized loss	148	39
Bank-issued trust preferred securities
Available-for-sale securities that had an unrealized loss:
Less than 12 months, fair value	0	0
Less than 12 months, unrealized loss	$ 0	$ 0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities	0	0
12 months or more, fair value	$ 1,838	$ 2,792
12 months or more, unrealized loss	$ 162	$ 207
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | securities	2	3
Total unrealized loss position, fair value	$ 1,838	$ 2,792
Total unrealized loss	$ 162	207
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | securities	2
Equity investment securities (a)
Available-for-sale securities that had an unrealized loss:
Less than 12 months, fair value		276
Less than 12 months, unrealized loss		$ 1
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year | securities		1
12 months or more, fair value		$ 112
12 months or more, unrealized loss		$ 64
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | securities		1
Total unrealized loss position, fair value		$ 388
Total unrealized loss		$ 65
Mortgage-backed securities, issued by US government sponsored agencies
Available-for-sale securities that had an unrealized loss:
Percentage of mortgage-backed securities in unrealized loss position for more than 12 months	99.00%
Mortgage-backed securities, privately issued
Available-for-sale securities that had an unrealized loss:
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | securities	2
Percentage of mortgage-backed securities in unrealized loss position for more than 12 months	1.00%
Fair value within book value	90.00%
Fair Value Less Than 90 Percent of Book Value [Member] | Mortgage-backed securities, privately issued
Available-for-sale securities that had an unrealized loss:
12 months or more, fair value	$ 145
Book value of privately issued mortgage-backed securities in unrealized loss position for more than 12 months	$ 217