Parent Company Financial Information - SUMMARY STATEMENTS OF CASH FLOWS (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income	$ 39,643	$ 28,392	$ 27,303	$ 28,002	$ 16,171	$ 20,232	$ 14,176	$ 9,521	$ 123,340	$ 60,100	$ 40,103
Adjustments to reconcile net income to cash used in operating activities:
Share-based compensation expense									9,033	5,809	2,729
Increase (decrease) in accrued expenses and other liabilities									1,388	5,193	(4,948)
Net cash (used in) provided by operating activities									298,688	83,777	63,447
Cash flows from financing activities:
Restricted stock surrendered and canceled									(1,669)	(1,258)	(126)
Proceeds from issuance of subordinated debentures									0	12,012	0
Net cash (used in) provided by financing activities									(52,756)	255,105	445,908
Net change in cash and cash equivalents									6,242	40,307	78,440
Cash and cash equivalents, beginning of year				197,164				156,857	197,164	156,857	78,417
Cash and cash equivalents, end of year	203,406				197,164				203,406	197,164	156,857
Corporation
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income									123,340	60,100	40,103
Adjustments to reconcile net income to cash used in operating activities:
Share-based compensation expense									9,033	5,809	2,729
Equity in undistributed earnings of subsidiaries and dividends from the bank									(132,459)	(68,323)	(44,901)
Increase (decrease) in accrued expenses and other liabilities									6,464	(365)	240
(Decrease) increase in current and deferred taxes									(3,682)	(896)	0
Decrease (increase) in other assets									(6,888)	1,714	4,794
Net cash (used in) provided by operating activities									(4,192)	(1,961)	2,965
Cash flows from financing activities:
Proceeds from issuance of common stock, net of issuance cost									0	0	0
Restricted stock surrendered and canceled									(1,669)	(1,258)	(125)
Proceeds from exercise of options and warrants									1,924	4,592	1,107
Capital contribution to Bank									0	600	7,765
Proceeds from issuance of subordinated debentures									0	0	0
Net cash (used in) provided by financing activities									255	3,934	8,747
Net change in cash and cash equivalents									(3,937)	1,973	11,712
Cash and cash equivalents, beginning of year				$ 17,097				$ 15,124	17,097	15,124	3,412
Cash and cash equivalents, end of year	$ 13,160				$ 17,097				$ 13,160	$ 17,097	$ 15,124