Fair Value Measurements - Assets and Liabilities Not Measured and Reported at Fair Value on a Recurring Basis or Nonrecurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Financial assets
Securities held to maturity	$ 0	$ 356,282
Securities available for sale	1,150,459	674,248
Mortgage loans held for sale	207,288	177,866
Mortgage servicing rights	35,930	26,302
Carrying Value
Financial assets
Cash and cash equivalents	332,200	306,224
Securities held to maturity		356,282
Securities available for sale	1,150,459	674,248
Mortgage loans held for sale	207,288	177,866
Loans, net	7,404,077	6,159,972
Mortgage servicing rights	35,930	26,302
Derivative instruments	8,569	9,108
Financial liabilities
Deposits	8,118,518	7,059,137
Short-term borrowings	384,230	109,676
Other long-term borrowings	111	147
Federal Home Loan Bank advances	7,760	8,542
Junior subordinated debentures	85,744	95,643
Subordinated notes	114,088	98,127
Derivative instruments	8,429	5,910
Fair Value
Financial assets
Cash and cash equivalents	332,200	306,224
Securities held to maturity		362,893
Securities available for sale	1,150,459	674,248
Mortgage loans held for sale	207,288	177,866
Loans, net	7,373,870	5,989,790
Mortgage servicing rights	41,822	32,064
Derivative instruments	8,569	9,108
Financial liabilities
Deposits	8,118,636	7,069,411
Short-term borrowings	384,230	109,676
Other long-term borrowings	111	147
Federal Home Loan Bank advances	8,005	8,777
Junior subordinated debentures	67,785	73,301
Subordinated notes	118,575	101,000
Derivative instruments	8,429	5,910
Fair Value | Level 1
Financial assets
Cash and cash equivalents	332,200	306,224
Securities held to maturity		0
Securities available for sale	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	6,290,726	5,438,384
Short-term borrowings	384,230	109,676
Other long-term borrowings	111	147
Federal Home Loan Bank advances	0	0
Junior subordinated debentures	0	0
Subordinated notes	0	0
Derivative instruments	0	0
Fair Value | Level 2
Financial assets
Cash and cash equivalents	0	0
Securities held to maturity		362,893
Securities available for sale	1,141,499	655,859
Mortgage loans held for sale	207,288	177,866
Loans, net	0	0
Mortgage servicing rights	0	0
Derivative instruments	8,569	9,108
Financial liabilities
Deposits	1,827,910	1,631,027
Short-term borrowings	0	0
Other long-term borrowings	0	0
Federal Home Loan Bank advances	8,005	8,777
Junior subordinated debentures	67,785	73,301
Subordinated notes	118,575	101,000
Derivative instruments	8,429	5,910
Fair Value | Level 3
Financial assets
Cash and cash equivalents	0	0
Securities held to maturity		0
Securities available for sale	8,960	18,389
Mortgage loans held for sale	0	0
Loans, net	7,373,870	5,989,790
Mortgage servicing rights	41,822	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