Condensed Financial Information (parent company only) - Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets
Investment securities	$ 1,142,195	$ 999,947
Premises and equipment	93,420	95,852
Interest receivable	40,881	37,130
Goodwill	445,355	445,355	$ 244,000
Cash surrender value of life insurance	224,939	223,557
Other assets	47,772	42,338
TOTAL ASSETS	9,884,716	9,367,478
Liabilities
Subordinated debentures and term loans	138,463	139,349
Interest payable	5,607	4,390
Other liabilities	45,295	52,708
Total Liabilities	8,476,456	8,064,015
Stockholders' equity	1,408,260	1,303,463	$ 901,657	$ 850,509
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	9,884,716	9,367,478
Parent
Assets
Cash	87,435	31,527
Investment in subsidiaries	1,459,036	1,411,360
Investment securities		31
Premises and equipment	1,158	1,252
Interest receivable	6	5
Goodwill	448	448
Cash surrender value of life insurance	810	787
Other assets	5,240	3,480
TOTAL ASSETS	1,554,133	1,448,890
Liabilities
Subordinated debentures and term loans	138,463	138,241
Interest payable	994	968
Other liabilities	6,416	6,218
Total Liabilities	145,873	145,427
Stockholders' equity	1,408,260	1,303,463
TOTAL LIABILITIES AND STOCKHOLDERS' EQUITY	$ 1,554,133	$ 1,448,890