(Parent Company Only) Financial Information - Summary of Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
ASSETS
Other assets	$ 110,246	$ 83,567
TOTAL ASSETS	5,810,129	4,680,932
LIABILITIES AND SHAREHOLDERS' EQUITY
Subordinated debt	70,521	70,241
Other liabilities	30,130	32,847
Shareholders' equity	689,664	435,397	$ 353,453	$ 312,651
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	5,810,129	4,680,932
Parent Company [Member]
ASSETS
Cash	1,154	648
Securities purchased under agreement to resell with subsidiary bank, maturing within 30 days	33,151	12,676
Investment in subsidiaries	711,973	494,809
Other assets	21,337	1,211
TOTAL ASSETS	767,615	509,344
LIABILITIES AND SHAREHOLDERS' EQUITY
Subordinated debt	70,521	70,241
Other liabilities	7,430	3,706
Shareholders' equity	689,664	435,397
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	$ 767,615	$ 509,344