Fair Value Measurements - Balances and Levels of Assets Measured at Fair Value on Recurring and Nonrecurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Financial assets:
Available-for-sale securities, at fair value	$ 543,282		$ 582,183
Mortgage servicing rights, net	63,046	$ 48,464	33,081	$ 46,291	$ 40,382	$ 29,711
Impaired loans	8,921		12,951
Fair Value, Measurements, Recurring
Financial assets:
Available-for-sale securities, at fair value	543,282		582,183
Loans held for sale	466,369		507,442
Mortgage servicing rights, net	63,046
Derivatives assets	10,316		19,745
Financial liabilities:
Derivatives liabilities	2,434		586
Fair Value, Measurements, Recurring | U.S. Government Agency Securities
Financial assets:
Available-for-sale securities, at fair value	992		985
Fair Value, Measurements, Recurring | Mortgage-backed Securities
Financial assets:
Available-for-sale securities, at fair value	418,794		443,908
Fair Value, Measurements, Recurring | Municipals, Tax Exempt
Financial assets:
Available-for-sale securities, at fair value	106,950		116,923
Fair Value, Measurements, Recurring | Treasury Securities
Financial assets:
Available-for-sale securities, at fair value	8,819		11,757
Fair Value, Measurements, Recurring | Equity Securities
Financial assets:
Available-for-sale securities, at fair value	7,727		8,610
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Financial assets:
Available-for-sale securities, at fair value	539,678		577,634
Loans held for sale	466,369		507,442
Derivatives assets	10,316		19,745
Financial liabilities:
Derivatives liabilities	2,434		586
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. Government Agency Securities
Financial assets:
Available-for-sale securities, at fair value	992		985
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Mortgage-backed Securities
Financial assets:
Available-for-sale securities, at fair value	418,794		443,908
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Municipals, Tax Exempt
Financial assets:
Available-for-sale securities, at fair value	106,950		116,923
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Treasury Securities
Financial assets:
Available-for-sale securities, at fair value	8,819		11,757
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Equity Securities
Financial assets:
Available-for-sale securities, at fair value	4,123		4,061
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Financial assets:
Available-for-sale securities, at fair value	3,604		4,549
Mortgage servicing rights, net	63,046
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Equity Securities
Financial assets:
Available-for-sale securities, at fair value	3,604		4,549
Fair Value, Measurements, Nonrecurring
Financial assets:
Mortgage servicing rights, net			32,070
Other real estate owned	8,704		2,315
Impaired loans	78,920		1,281
Fair Value, Measurements, Nonrecurring | Commercial and Industrial
Financial assets:
Impaired loans	2,659		542
Fair Value, Measurements, Nonrecurring | Consumer and Other
Financial assets:
Impaired loans	26,800		1
Fair Value, Measurements, Nonrecurring | 1-to-4 Family Mortgage | Residential Real Estate
Financial assets:
Impaired loans	22,948		103
Fair Value, Measurements, Nonrecurring | Owner Occupied | Commercial Real Estate
Financial assets:
Impaired loans			635
Fair Value, Measurements, Nonrecurring | Non-Owner Occupied | Commercial Real Estate
Financial assets:
Impaired loans	13,912
Fair Value, Measurements, Nonrecurring | Significant Unobservable Inputs (Level 3)
Financial assets:
Mortgage servicing rights, net			32,070
Other real estate owned	8,704		2,315
Impaired loans	78,920		1,281
Fair Value, Measurements, Nonrecurring | Significant Unobservable Inputs (Level 3) | Commercial and Industrial
Financial assets:
Impaired loans	2,659		542
Fair Value, Measurements, Nonrecurring | Significant Unobservable Inputs (Level 3) | Consumer and Other
Financial assets:
Impaired loans	26,800		1
Fair Value, Measurements, Nonrecurring | Significant Unobservable Inputs (Level 3) | Construction Loans | Commercial and Industrial
Financial assets:
Impaired loans	4,295
Fair Value, Measurements, Nonrecurring | Significant Unobservable Inputs (Level 3) | 1-to-4 Family Mortgage | Residential Real Estate
Financial assets:
Impaired loans	22,948		103
Fair Value, Measurements, Nonrecurring | Significant Unobservable Inputs (Level 3) | Owner Occupied | Commercial Real Estate
Financial assets:
Impaired loans	8,306		$ 635
Fair Value, Measurements, Nonrecurring | Significant Unobservable Inputs (Level 3) | Non-Owner Occupied | Commercial Real Estate
Financial assets:
Impaired loans	$ 13,912