Goodwill and Intangible Assets, Summary of Core Deposit and Other Intangibles (Details) - USD ($)	3 Months Ended		12 Months Ended
	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary of core deposit intangibles and other intangibles
Additions during the period	$ 2,000,000	$ 162,000
Amortization of other intangible assets			$ 1,959,000	$ 2,093,000	$ 3,094,000
Core Deposit Intangibles
Summary of core deposit intangibles and other intangibles
Gross carrying amount	4,385,000		4,385,000	4,385,000	19,545,000
Accumulated amortization	(4,385,000)		(4,385,000)	(4,273,000)	(19,152,000)
Total Estimated Amortization Expense	0		0	112,000	393,000
Amortization of other intangible assets			112,000	281,000	1,404,000
Other Intangibles
Summary of core deposit intangibles and other intangibles
Gross carrying amount	34,572,000		34,572,000	32,410,000	31,398,000
Accumulated amortization	(18,992,000)		(18,992,000)	(17,145,000)	(15,333,000)
Total Estimated Amortization Expense	$ 15,580,000		15,580,000	15,265,000	16,065,000
Additions during the period			2,162,000	1,012,000	12,115,000
Amortization of other intangible assets			$ 1,847,000	$ 1,812,000	$ 1,690,000