Tax Credit Investments - Income Statement Disclosures (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Components of Income Tax Expense
Affordable housing tax credits and other tax benefits	$ 1,429	$ 1,271	$ 3,250	$ 2,555
Other tax credit investment credits and tax benefits	5,680	8,680	11,165	14,966
Total reduction in income tax expense	7,109	9,951	14,415	17,521
Non-Interest Expenses
Amortization of Tax Credit Investments
Affordable housing tax credit investment losses	(319)	358	667	754
Affordable housing tax credit investment impairment losses	515	130	1,102	254
Other tax credit investment losses	1,253	1,060	1,790	1,827
Other tax credit investment impairment losses	3,021	6,184	6,185	10,221
Total amortization of tax credit investments recorded in non-interest expense	$ 4,470	$ 7,732	$ 9,744	$ 13,056