Allowance for Loan Losses - Investment in Loans, Net of Unearned Income on Impairment Methodology (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Investment in loans, net of unearned income on impairment methodology
Individually evaluated for impairment	$ 50,046	$ 35,278
Collectively evaluated for impairment	9,075,624	8,825,597
Loans, net of unearned income	9,313,784	9,083,129
Purchased with deteriorated credit quality
Investment in loans, net of unearned income on impairment methodology
Purchased with deteriorated credit quality	188,114	222,254
Commercial
Investment in loans, net of unearned income on impairment methodology
Individually evaluated for impairment	8,124	2,445
Collectively evaluated for impairment	1,289,326	1,264,324
Loans, net of unearned income	1,328,560	1,295,912
Commercial | Purchased with deteriorated credit quality
Investment in loans, net of unearned income on impairment methodology
Purchased with deteriorated credit quality	31,110	29,143
Real estate – construction
Investment in loans, net of unearned income on impairment methodology
Individually evaluated for impairment	12,380	10,043
Collectively evaluated for impairment	803,710	730,625
Loans, net of unearned income	816,695	740,668
Real estate – construction | Purchased with deteriorated credit quality
Investment in loans, net of unearned income on impairment methodology
Purchased with deteriorated credit quality	605	0
Real estate – 1-4 family mortgage
Investment in loans, net of unearned income on impairment methodology
Individually evaluated for impairment	17,332	14,238
Collectively evaluated for impairment	2,742,677	2,732,862
Loans, net of unearned income	2,797,633	2,795,343
Real estate – 1-4 family mortgage | Purchased with deteriorated credit quality
Investment in loans, net of unearned income on impairment methodology
Purchased with deteriorated credit quality	37,624	48,243
Real estate – commercial mortgage
Investment in loans, net of unearned income on impairment methodology
Individually evaluated for impairment	11,755	8,059
Collectively evaluated for impairment	3,894,838	3,903,012
Loans, net of unearned income	4,022,375	4,051,509
Real estate – commercial mortgage | Purchased with deteriorated credit quality
Investment in loans, net of unearned income on impairment methodology
Purchased with deteriorated credit quality	115,782	140,438
Installment and Other
Investment in loans, net of unearned income on impairment methodology
Individually evaluated for impairment	455	493
Collectively evaluated for impairment	345,073	194,774
Loans, net of unearned income	348,521	199,697
Installment and Other | Purchased with deteriorated credit quality
Investment in loans, net of unearned income on impairment methodology
Purchased with deteriorated credit quality	$ 2,993	$ 4,430