Parent Company Financial Information - SUMMARY STATEMENTS OF CASH FLOWS (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Parent Company Financial Information
Net income	$ 16,171	$ 20,232	$ 14,176	$ 9,521	$ 11,953	$ 9,227	$ 10,369	$ 8,554	$ 60,100	$ 40,103	$ 25,515
Adjustments to reconcile net income to cash used in operating activities:
Share-based compensation expense									5,809	2,729	1,165
Increase (decrease) in accrued expenses and other liabilities									5,003	(4,428)	6,786
Net cash (used in) provided by operating activities									83,999	63,447	23,669
Cash flows from financing activities:
Repurchase of common stock									(1,258)	(126)	(116)
Proceeds from issuance of subordinated debentures									12,012	0	0
Net cash provided by financing activities									255,087	445,908	275,103
Net increase (decrease) in cash and cash equivalents									43,207	78,440	(32,508)
Cash and cash equivalents, beginning of year				156,857				78,417	156,857	78,417	110,925
Cash and cash equivalents, end of year	200,064				156,857				200,064	156,857	78,417
Corporation
Parent Company Financial Information
Net income									60,100	40,103	25,515
Adjustments to reconcile net income to cash used in operating activities:
Share-based compensation expense									5,809	2,729	1,165
Equity in undistributed earnings of subsidiaries and dividends from the bank									(68,323)	(44,901)	(29,473)
Increase (decrease) in accrued expenses and other liabilities									(365)	240	166
(Decrease) increase in current and deferred taxes									(896)	0	3,566
Decrease (increase) in other assets									1,714	4,794	(6,893)
Net cash (used in) provided by operating activities									(1,961)	2,965	(5,954)
Cash flows from financing activities:
Proceeds from issuance of common stock, net of issuance cost									0	0	0
Repurchase of common stock									(1,258)	(125)	(116)
Proceeds from exercise of options and warrants									4,592	1,107	758
Capital contribution to Bank									600	7,765	(10,000)
Proceeds from issuance of subordinated debentures									0	0	0
Net cash provided by financing activities									3,934	8,747	(9,358)
Net increase (decrease) in cash and cash equivalents									1,973	11,712	(15,312)
Cash and cash equivalents, beginning of year				$ 15,124				$ 3,412	15,124	3,412	18,724
Cash and cash equivalents, end of year	$ 17,097				$ 15,124				$ 17,097	$ 15,124	$ 3,412