Fair Value Measurements (Details 7) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair values of defined benefit pension plan assets by category of the firm
Securities held to maturity	$ 0	$ 356,282
Securities available for sale, at fair value	671,488	674,248
Mortgage loans held for sale	108,316	177,866
Quoted Prices In Active Markets for Identical Assets (Level 1)
Fair values of defined benefit pension plan assets by category of the firm
Cash and cash equivalents	281,453	306,224
Securities held to maturity		0
Securities available for sale, at fair value	0	0
Mortgage loans held for sale	0	0
Loans, net	0	0
Mortgage servicing rights	0	0
Derivative instruments	0	0
Financial liabilities
Deposits	6,114,391	5,438,384
Short-term borrowings	89,814	109,676
Other long-term borrowings	98	147
Federal Home Loan Bank advances	0	0
Junior subordinated debentures	0	0
Subordinated notes	0	0
Derivative instruments	0	0
Significant Other Observable Inputs (Level 2)
Fair values of defined benefit pension plan assets by category of the firm
Cash and cash equivalents	0	0
Securities held to maturity		362,893
Securities available for sale, at fair value	662,100	655,859
Mortgage loans held for sale	108,316	177,866
Loans, net	0	0
Mortgage servicing rights	0	0
Derivative instruments	5,977	9,108
Financial liabilities
Deposits	1,809,085	1,631,027
Short-term borrowings	0	0
Other long-term borrowings	0	0
Federal Home Loan Bank advances	7,661	8,777
Junior subordinated debentures	69,702	73,301
Subordinated notes	118,650	101,000
Derivative instruments	6,039	5,910
Significant Unobservable Inputs (Level 3)
Fair values of defined benefit pension plan assets by category of the firm
Cash and cash equivalents	0	0
Securities held to maturity		0
Securities available for sale, at fair value	9,388	18,389
Mortgage loans held for sale	0	0
Loans, net	7,514,185	5,989,790
Mortgage servicing rights	47,868	32,064
Derivative instruments	0	0
Financial liabilities
Deposits	0	0
Short-term borrowings	0	0
Other long-term borrowings	0	0
Federal Home Loan Bank advances	0	0
Junior subordinated debentures	0	0
Subordinated notes	0	0
Derivative instruments	0	0
Carrying Value
Fair values of defined benefit pension plan assets by category of the firm
Cash and cash equivalents	281,453	306,224
Securities held to maturity		356,282
Securities available for sale, at fair value	671,488	674,248
Mortgage loans held for sale	108,316	177,866
Loans, net	7,574,111	6,159,972
Mortgage servicing rights	39,339	26,302
Derivative instruments	5,977	9,108
Financial liabilities
Deposits	7,921,075	7,059,137
Short-term borrowings	89,814	109,676
Other long-term borrowings	98	147
Federal Home Loan Bank advances	7,493	8,542
Junior subordinated debentures	85,881	95,643
Subordinated notes	114,074	98,127
Derivative instruments	6,039	5,910
Fair Value
Fair values of defined benefit pension plan assets by category of the firm
Cash and cash equivalents	281,453	306,224
Securities held to maturity		362,893
Securities available for sale, at fair value	671,488	674,248
Mortgage loans held for sale	108,316	177,866
Loans, net	7,514,185	5,989,790
Mortgage servicing rights	47,868	32,064
Derivative instruments	5,977	9,108
Financial liabilities
Deposits	7,923,476	7,069,411
Short-term borrowings	89,814	109,676
Other long-term borrowings	98	147
Federal Home Loan Bank advances	7,661	8,777
Junior subordinated debentures	69,702	73,301
Subordinated notes	118,650	101,000
Derivative instruments	$ 6,039	$ 5,910