Fair Value Measurements (Recurring Basis) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	$ 1,963,546	$ 1,234,964
Loan servicing rights	63,841	48,085	$ 0
U.S. Treasury securities
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value		5,793
Government sponsored agencies
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	202,916	215,011
State and political subdivisions
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	345,970	300,088
Residential mortgage-backed securities
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	150,131	272,282
Collateralized mortgage obligations
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	1,033,845	320,025
Corporate bonds
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	192,794	89,474
Preferred stock and trust preferred securities
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	37,890	32,291
Recurring
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	1,963,546	1,234,964
Loans held-for-sale	52,133	81,830
Loan servicing rights	63,841	48,085
Derivative assets	18,681	8,215
Total assets at fair value	2,098,201	1,373,094
Derivative liabilities	12,357	6,359
Total liabilities at fair value	12,357	6,359
Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	5,793
Loans held-for-sale	0	0
Loan servicing rights	0	0
Derivative assets	0	0
Total assets at fair value	0	5,793
Derivative liabilities	0	0
Total liabilities at fair value	0	0
Recurring | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	1,963,546	1,229,171
Loans held-for-sale	52,133	81,830
Loan servicing rights	0	0
Derivative assets	18,681	8,215
Total assets at fair value	2,034,360	1,319,216
Derivative liabilities	12,357	6,359
Total liabilities at fair value	12,357	6,359
Recurring | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0
Loans held-for-sale	0	0
Loan servicing rights	63,841	48,085
Derivative assets	0	0
Total assets at fair value	63,841	48,085
Derivative liabilities	0	0
Total liabilities at fair value	0	0
Recurring | Customer-initiated derivatives
Summary of assets measured at fair value on a recurring basis
Derivative assets	9,376	4,406
Derivative liabilities	10,139	4,141
Recurring | Customer-initiated derivatives | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Derivative assets	0	0
Derivative liabilities	0	0
Recurring | Customer-initiated derivatives | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Derivative assets	9,376	4,406
Derivative liabilities	10,139	4,141
Recurring | Customer-initiated derivatives | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Derivative assets	0	0
Derivative liabilities	0	0
Recurring | Forward contracts related to mortgage loans to be delivered for sale
Summary of assets measured at fair value on a recurring basis
Derivative assets		635
Derivative liabilities	34
Recurring | Forward contracts related to mortgage loans to be delivered for sale | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Derivative assets		0
Derivative liabilities	0
Recurring | Forward contracts related to mortgage loans to be delivered for sale | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Derivative assets		635
Derivative liabilities	34
Recurring | Forward contracts related to mortgage loans to be delivered for sale | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Derivative assets		0
Derivative liabilities	0
Recurring | Interest rate lock commitments
Summary of assets measured at fair value on a recurring basis
Derivative assets	1,222	956
Recurring | Interest rate lock commitments | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Derivative assets	0	0
Recurring | Interest rate lock commitments | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Derivative assets	1,222	956
Recurring | Interest rate lock commitments | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Derivative assets	0	0
Recurring | Power Equity CD
Summary of assets measured at fair value on a recurring basis
Derivative assets	2,184	2,218
Derivative liabilities	2,184	2,218
Recurring | Power Equity CD | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Derivative assets	0	0
Derivative liabilities	0	0
Recurring | Power Equity CD | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Derivative assets	2,184	2,218
Derivative liabilities	2,184	2,218
Recurring | Power Equity CD | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Derivative assets	0	0
Derivative liabilities	0	0
Recurring | Risk management derivatives
Summary of assets measured at fair value on a recurring basis
Derivative assets	5,899
Recurring | Risk management derivatives | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Derivative assets	0
Recurring | Risk management derivatives | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Derivative assets	5,899
Recurring | Risk management derivatives | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Derivative assets	0
Recurring | U.S. Treasury securities
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value		5,793
Recurring | U.S. Treasury securities | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value		5,793
Recurring | U.S. Treasury securities | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value		0
Recurring | U.S. Treasury securities | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value		0
Recurring | Government sponsored agencies
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	202,916	215,011
Recurring | Government sponsored agencies | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0
Recurring | Government sponsored agencies | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	202,916	215,011
Recurring | Government sponsored agencies | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0
Recurring | State and political subdivisions
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	345,970	300,088
Recurring | State and political subdivisions | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0
Recurring | State and political subdivisions | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	345,970	300,088
Recurring | State and political subdivisions | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0
Recurring | Mortgage-backed securities
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	150,131
Recurring | Mortgage-backed securities | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0
Recurring | Mortgage-backed securities | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	150,131
Recurring | Mortgage-backed securities | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0
Recurring | Residential mortgage-backed securities
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value		272,282
Recurring | Residential mortgage-backed securities | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value		0
Recurring | Residential mortgage-backed securities | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value		272,282
Recurring | Residential mortgage-backed securities | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value		0
Recurring | Collateralized mortgage obligations
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	1,033,845	320,025
Recurring | Collateralized mortgage obligations | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0
Recurring | Collateralized mortgage obligations | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	1,033,845	320,025
Recurring | Collateralized mortgage obligations | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0
Recurring | Corporate bonds
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	192,794	89,474
Recurring | Corporate bonds | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0
Recurring | Corporate bonds | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	192,794	89,474
Recurring | Corporate bonds | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0
Recurring | Preferred stock and trust preferred securities
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	37,890	32,291
Recurring | Preferred stock and trust preferred securities | Quoted Prices In Active Markets for Identical Assets (Level 1)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	0	0
Recurring | Preferred stock and trust preferred securities | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	37,890	32,291
Recurring | Preferred stock and trust preferred securities | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	$ 0	$ 0