Business Combinations - fair value of the assets purchased, including goodwill, and liabilities (Details) - USD ($)	1 Months Ended	3 Months Ended	12 Months Ended
	Jul. 17, 2015	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jun. 03, 2016	Mar. 11, 2016
Assets:
Loans, net						$ 314,000,000
Goodwill		$ 25,211,000	$ 64,649,000	$ 25,211,000
Liabilities:
Deposits						63,000,000
Bargain purchase gain	$ (416,000)		$ 0	$ 416,000	$ 0
Bank shares, Inc [Member]
Liabilities:
Bargain purchase gain		$ 416,000
Bank shares, Inc [Member] | Measurement Period Adjustments [Member]
Assets:
Cash	0
Investment securities	0
Loans, net	1,304,000
Fixed assets	0
OREO	437,000
Core deposit intangibles	0
Goodwill	(555,000)
Other assets	(770,000)
Total assets acquired	416,000
Liabilities:
Deposits	0
Borrowings	0
Subordinated debt	0
Other liabilities	0
Total liabilities assumed	0
Bank shares, Inc [Member] | Scenario, Previously Reported [Member]
Assets:
Cash	34,408,000
Investment securities	46,366,000
Loans, net	109,988,000
Fixed assets	4,191,000
OREO	2,424,000
Core deposit intangibles	2,564,000
Goodwill	555,000
Other assets	14,163,000
Total assets acquired	214,659,000
Liabilities:
Deposits	188,469,000
Borrowings	1,658,000
Subordinated debt	5,151,000
Other liabilities	728,000
Total liabilities assumed	196,006,000
Bank shares, Inc [Member] | Restatement Adjustment [Member]
Assets:
Cash	34,408,000
Investment securities	46,366,000
Loans, net	111,292,000
Fixed assets	4,191,000
OREO	2,861,000
Core deposit intangibles	2,564,000
Goodwill	0
Other assets	13,393,000
Total assets acquired	215,075,000
Liabilities:
Deposits	188,469,000
Borrowings	1,658,000
Subordinated debt	5,151,000
Other liabilities	728,000
Total liabilities assumed	$ 196,006,000
Floridian Financial Group, Inc [Member] | Measurement Period Adjustments [Member]
Assets:
Cash							$ 0
Investment securities							95,000
Loans, net							(2,112,000)
Fixed assets							(628,000)
Core deposit intangibles							0
Goodwill							1,647,000
Other assets							998,000
Total assets acquired							0
Liabilities:
Deposits							0
Other liabilities							0
Total liabilities assumed							0
Floridian Financial Group, Inc [Member] | Scenario, Previously Reported [Member]
Assets:
Cash							28,243,000
Investment securities							66,912,000
Loans, net							268,249,000
Fixed assets							7,801,000
Core deposit intangibles							3,375,000
Goodwill							29,985,000
Other assets							12,879,000
Total assets acquired							417,444,000
Liabilities:
Deposits							337,341,000
Other liabilities							2,492,000
Total liabilities assumed							339,833,000
Floridian Financial Group, Inc [Member] | Restatement Adjustment [Member]
Assets:
Cash							28,243,000
Investment securities							67,007,000
Loans, net							266,137,000
Fixed assets							7,173,000
Core deposit intangibles							3,375,000
Goodwill							31,632,000
Other assets							13,877,000
Total assets acquired							417,444,000
Liabilities:
Deposits							337,341,000
Other liabilities							2,492,000
Total liabilities assumed							$ 339,833,000
BMO Harris Bank [Member] | Measurement Period Adjustments [Member]
Assets:
Cash						0
Loans, net						0
Fixed assets						0
Core deposit intangibles						(135,000)
Goodwill						163,000
Other assets						(28,000)
Total assets acquired						0
Liabilities:
Deposits						0
Other liabilities						0
Total liabilities assumed						0
BMO Harris Bank [Member] | Scenario, Previously Reported [Member]
Assets:
Cash						234,094,000
Loans, net						62,671,000
Fixed assets						3,715,000
Core deposit intangibles						5,223,000
Goodwill						7,645,000
Other assets						952,000
Total assets acquired						314,300,000
Liabilities:
Deposits						314,248,000
Other liabilities						52,000
Total liabilities assumed						314,300,000
BMO Harris Bank [Member] | Restatement Adjustment [Member]
Assets:
Cash						234,094,000
Loans, net						62,671,000
Fixed assets						3,715,000
Core deposit intangibles						5,088,000
Goodwill						7,808,000
Other assets						924,000
Total assets acquired						314,300,000
Liabilities:
Deposits						314,248,000
Other liabilities						52,000
Total liabilities assumed						$ 314,300,000