Portfolio Loans - Summary of Recorded Investment by Risk Category of Portfolio Loans by Portfolio Class and Category (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans, including unearned loan fees	$ 4,097,050	$ 3,158,161
Non-Covered Loans
Financing Receivable, Recorded Investment [Line Items]
Total	4,024,221	3,119,154
Loans, including unearned loan fees	4,022,896	3,118,392
Non-Covered Loans | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total	1,918,720	1,632,714
Non-Covered Loans | CRE - investor owned
Financing Receivable, Recorded Investment [Line Items]
Total	769,275	544,808
Non-Covered Loans | CRE - owner occupied
Financing Receivable, Recorded Investment [Line Items]
Total	554,589	350,148
Non-Covered Loans | Construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total	303,091	194,542
Non-Covered Loans | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Total	341,312	240,760
Non-Covered Loans | Consumer and other
Financing Receivable, Recorded Investment [Line Items]
Total	137,234	156,182
Loans, including unearned loan fees	135,909	155,420
Pass (1-6) | Non-Covered Loans
Financing Receivable, Recorded Investment [Line Items]
Loans, including unearned loan fees	3,794,940	2,909,234
Pass (1-6) | Non-Covered Loans | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total	1,769,102	1,499,114
Pass (1-6) | Non-Covered Loans | CRE - investor owned
Financing Receivable, Recorded Investment [Line Items]
Total	514,616	306,658
Pass (1-6) | Non-Covered Loans | CRE - owner occupied
Financing Receivable, Recorded Investment [Line Items]
Total	754,010	530,494
Pass (1-6) | Non-Covered Loans | Construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total	292,766	185,505
Pass (1-6) | Non-Covered Loans | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Total	329,742	233,479
Pass (1-6) | Non-Covered Loans | Consumer and other
Financing Receivable, Recorded Investment [Line Items]
Loans, including unearned loan fees	134,704	153,984
Watch (7) | Non-Covered Loans
Financing Receivable, Recorded Investment [Line Items]
Loans, including unearned loan fees	152,923	116,686
Watch (7) | Non-Covered Loans | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total	94,002	57,416
Watch (7) | Non-Covered Loans | CRE - investor owned
Financing Receivable, Recorded Investment [Line Items]
Total	34,440	39,249
Watch (7) | Non-Covered Loans | CRE - owner occupied
Financing Receivable, Recorded Investment [Line Items]
Total	10,840	10,449
Watch (7) | Non-Covered Loans | Construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total	9,983	6,575
Watch (7) | Non-Covered Loans | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Total	3,648	2,997
Watch (7) | Non-Covered Loans | Consumer and other
Financing Receivable, Recorded Investment [Line Items]
Loans, including unearned loan fees	10	0
Substandard (8) | Non-Covered Loans
Financing Receivable, Recorded Investment [Line Items]
Loans, including unearned loan fees	75,033	92,472
Substandard (8) | Non-Covered Loans | Commercial and industrial
Financing Receivable, Recorded Investment [Line Items]
Total	55,616	76,184
Substandard (8) | Non-Covered Loans | CRE - investor owned
Financing Receivable, Recorded Investment [Line Items]
Total	5,533	4,241
Substandard (8) | Non-Covered Loans | CRE - owner occupied
Financing Receivable, Recorded Investment [Line Items]
Total	4,425	3,865
Substandard (8) | Non-Covered Loans | Construction and land development
Financing Receivable, Recorded Investment [Line Items]
Total	342	2,462
Substandard (8) | Non-Covered Loans | Residential real estate
Financing Receivable, Recorded Investment [Line Items]
Total	7,922	4,284
Substandard (8) | Non-Covered Loans | Consumer and other
Financing Receivable, Recorded Investment [Line Items]
Loans, including unearned loan fees	$ 1,195	$ 1,436