Fair Value Measurements - Assets on a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	$ 1,767,478		$ 1,234,964
Loan servicing rights	64,522	$ 64,604	48,085
U.S. Treasury securities
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	5,793		5,793
Government sponsored agencies
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	247,474		215,011
State and political subdivisions
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	292,035		300,088
Residential mortgage-backed securities
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	292,912		272,282
Collateralized mortgage obligations
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	733,187		320,025
Corporate bonds
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	158,168		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	37,909		32,291
Recurring
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	1,767,478		1,234,964
Loans held-for-sale	65,371		81,830
Loan servicing rights	64,522		48,085
Total derivatives	13,536		8,215
Total assets measured at fair value on a recurring basis	1,910,907		1,373,094
Total derivatives	11,496		6,359
Total liabilities at fair value	11,496		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	5,793		5,793
Loans held-for-sale	0		0
Loan servicing rights	0		0
Total derivatives	0		0
Total assets measured at fair value on a recurring basis	5,793		5,793
Total derivatives	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	1,761,685		1,229,171
Loans held-for-sale	65,371		81,830
Loan servicing rights	0		0
Total derivatives	13,536		8,215
Total assets measured at fair value on a recurring basis	1,840,592		1,319,216
Total derivatives	11,496		6,359
Total liabilities at fair value	11,496		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	64,522		48,085
Total derivatives	0		0
Total assets measured at fair value on a recurring basis	64,522		48,085
Total derivatives	0		0
Total liabilities at fair value	0		0
Recurring | Customer-initiated derivatives
Summary of assets measured at fair value on a recurring basis
Total derivatives	8,636		4,406
Total derivatives	9,152		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
Total derivatives	0		0
Total derivatives	0		0
Recurring | Customer-initiated derivatives | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Total derivatives	8,636		4,406
Total derivatives	9,152		4,141
Recurring | Customer-initiated derivatives | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Total derivatives	0		0
Total derivatives	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
Total derivatives	617		635
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
Total derivatives	0		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
Total derivatives	617		635
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
Total derivatives	0		0
Recurring | Interest rate lock commitments
Summary of assets measured at fair value on a recurring basis
Total derivatives	1,997		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
Total derivatives	0		0
Recurring | Interest rate lock commitments | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Total derivatives	1,997		956
Recurring | Interest rate lock commitments | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Total derivatives	0		0
Recurring | Power Equity CD
Summary of assets measured at fair value on a recurring basis
Total derivatives	2,062		2,218
Total derivatives	2,062		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
Total derivatives	0		0
Total derivatives	0		0
Recurring | Power Equity CD | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Total derivatives	2,062		2,218
Total derivatives	2,062		2,218
Recurring | Power Equity CD | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Total derivatives	0		0
Total derivatives	0		0
Recurring | Risk management derivatives
Summary of assets measured at fair value on a recurring basis
Total derivatives	224
Total derivatives	282
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
Total derivatives	0
Total derivatives	0
Recurring | Risk management derivatives | Significant Other Observable Inputs (Level 2)
Summary of assets measured at fair value on a recurring basis
Total derivatives	224
Total derivatives	282
Recurring | Risk management derivatives | Significant Unobservable Inputs (Level 3)
Summary of assets measured at fair value on a recurring basis
Total derivatives	0
Total derivatives	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		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		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		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		0
Recurring | Government sponsored agencies
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	247,474		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	247,474		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	292,035		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	292,035		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 | Residential mortgage-backed securities
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	292,912		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		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	292,912		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		0
Recurring | Collateralized mortgage obligations
Summary of assets measured at fair value on a recurring basis
Available-for-sale, at fair value	733,187		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	733,187		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	158,168		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	158,168		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	37,909		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	37,909		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