Income Taxes Text Details Income Tax Components (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Expense Components [Line Items]
Other Information Pertaining to Income Taxes		On December 22, 2017, H.R. 1, the Tax Act, was enacted by the U.S. government. Substantially all of the provisions of the Tax Act are effective as of January 1, 2018. The Tax Act includes significant changes to the Internal Revenue Code of 1986, as amended, including amendments which significantly change the taxation of business entities. The more significant changes in the Tax Act that impact the Company are the reduction in the federal corporate tax rate from 35% to 21% and the changes to the deductibility of executive compensation, both of which are effective as of January 1, 2018. Under ASC 740, the tax effects of changes in tax laws must be recognized in the period in which the law is enacted, or December 22, 2017 for the Tax Act. ASC 740 also requires deferred tax assets and liabilities to be measured at the enacted tax rate expected to apply when temporary differences are to be realized or settled. The Company re-measured its deferred tax assets and liabilities at the 21% federal corporate tax rate, reevaluated its investments in affordable housing projects using the 21% federal corporate tax rate, and reduced its deferred tax assets associated with executive compensation that is no longer deductible.
Federal	$ 12,900
Effective Income Tax Rate Reconciliation, Other Reconciling Items, Amount		$ 700
Increase (Decrease) in Deferred Income Taxes		26,400
Deferred Income Tax Expense (Benefit)		22,845	$ 2,777	$ (4,575)
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount		11,800
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	900	900	800	800
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense		0	0	0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	$ 0	0	0	0
Internal Revenue Service (IRS) [Member]
Income Tax Expense Components [Line Items]
Effective Income Tax Rate Reconciliation, Other Reconciling Items, Amount				1,200
State and Local Jurisdiction [Member]
Income Tax Expense Components [Line Items]
Effective Income Tax Rate Reconciliation, Other Reconciling Items, Amount				200
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount				500
Income Tax Expense Components, Continuing Operations [Member]
Income Tax Expense Components [Line Items]
Federal		17,176	20,237	25,631
Deferred Income Tax Expense (Benefit)		$ 22,511	$ 2,948	$ (4,422)