Investment Securities Available-for-sale Securities with Unrealized Losses (Details)	12 Months Ended
	Dec. 31, 2016 USD ($) securities	Dec. 31, 2015 USD ($) securities
Available-for-sale securities that had an unrealized loss:
Fair value of securities in unrealized loss position less than 12 months	$ 458,622,000	$ 320,460,000
Unrealized loss less than 12 months	$ 8,848,000	$ 4,018,000
Number of securities at an unrealized loss position less than 12 months | securities	141	90
Fair value of securities in unrealized loss more than 12 months	$ 49,378,000	$ 104,915,000
Unrealized loss more than 12 months	$ 2,924,000	$ 4,781,000
Number of securities at an unrealized loss position more than 12 months | securities	26	38
Fair value of securities in unrealized loss	$ 508,000,000	$ 425,375,000
Unrealized loss	11,772,000	8,799,000
Other-than-temporary impairments	$ 0
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 less than 12 months	99.00%
Mortgage-backed securities privately issued
Available-for-sale securities that had an unrealized loss:
Number of securities at an unrealized loss position less than 12 months | securities	2
Percentage of mortgage-backed securities in unrealized loss position for less than 12 months	1.00%
Fair value within book value	90.00%
States and political subdivisions
Available-for-sale securities that had an unrealized loss:
Fair value of securities in unrealized loss position less than 12 months	$ 23,501,000	7,662,000
Unrealized loss less than 12 months	$ 263,000	$ 38,000
Number of securities at an unrealized loss position less than 12 months | securities	28	8
Fair value of securities in unrealized loss more than 12 months	$ 0	$ 213,000
Unrealized loss more than 12 months	$ 0	$ 6,000
Number of securities at an unrealized loss position more than 12 months | securities	0	1
Fair value of securities in unrealized loss	$ 23,501,000	$ 7,875,000
Unrealized loss	263,000	44,000
Residential mortgage-backed securities
Available-for-sale securities that had an unrealized loss:
Fair value of securities in unrealized loss position less than 12 months	427,088,000	303,549,000
Unrealized loss less than 12 months	$ 8,495,000	$ 3,902,000
Number of securities at an unrealized loss position less than 12 months | securities	108	76
Fair value of securities in unrealized loss more than 12 months	$ 46,631,000	$ 102,090,000
Unrealized loss more than 12 months	$ 2,498,000	$ 4,214,000
Number of securities at an unrealized loss position more than 12 months | securities	22	33
Fair value of securities in unrealized loss	$ 473,719,000	$ 405,639,000
Unrealized loss	10,993,000	8,116,000
Commercial mortgage-backed securities
Available-for-sale securities that had an unrealized loss:
Fair value of securities in unrealized loss position less than 12 months	7,770,000	6,682,000
Unrealized loss less than 12 months	$ 87,000	$ 44,000
Number of securities at an unrealized loss position less than 12 months | securities	4	3
Fair value of securities in unrealized loss more than 12 months	$ 0	$ 0
Unrealized loss more than 12 months	$ 0	$ 0
Number of securities at an unrealized loss position more than 12 months | securities	0	0
Fair value of securities in unrealized loss	$ 7,770,000	$ 6,682,000
Unrealized loss	87,000	44,000
Bank-issued trust preferred securities
Available-for-sale securities that had an unrealized loss:
Fair value of securities in unrealized loss position less than 12 months	0	2,129,000
Unrealized loss less than 12 months	$ 0	$ 19,000
Number of securities at an unrealized loss position less than 12 months | securities	0	1
Fair value of securities in unrealized loss more than 12 months	$ 2,637,000	$ 2,506,000
Unrealized loss more than 12 months	$ 361,000	$ 492,000
Number of securities at an unrealized loss position more than 12 months | securities	3	3
Fair value of securities in unrealized loss	$ 2,637,000	$ 4,635,000
Unrealized loss	$ 361,000	511,000
Number of available-for-sale securities in unrealized loss position | securities	3
Equity securities
Available-for-sale securities that had an unrealized loss:
Fair value of securities in unrealized loss position less than 12 months	$ 263,000	438,000
Unrealized loss less than 12 months	$ 3,000	$ 15,000
Number of securities at an unrealized loss position less than 12 months | securities	1	2
Fair value of securities in unrealized loss more than 12 months	$ 110,000	$ 106,000
Unrealized loss more than 12 months	$ 65,000	$ 69,000
Number of securities at an unrealized loss position more than 12 months | securities	1	1
Fair value of securities in unrealized loss	$ 373,000	$ 544,000
Unrealized loss	68,000	$ 84,000
Fair Value Less Than 90 Percent of Book Value | Mortgage-backed securities privately issued
Available-for-sale securities that had an unrealized loss:
Fair value of securities in unrealized loss more than 12 months	500,000
Mortgage-backed securities in unrealized loss position for less than 12 months, aggregate book value	$ 700,000