Condensed Financial Information (Parent Company Only) (Cash flows) (Details) - USD ($) $ in Thousands		12 Months Ended
	Nov. 02, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities:
Net income		$ 54,684	$ 33,127	$ 28,383
Net cash provided by (used in) operating activities		(175,886)	(149,771)	118,328
Investing activities:
Other investing activities		189	(295)
Net cash used in investing activities		(523,137)	(265,302)	(349,333)
Financing activities:
Dividends paid		(7,950)	(6,224)	(4,222)
Proceeds from issuance of common stock	$ 106,200	106,245		3,941
Proceeds from issuance of preferred stock			31,581	10,000
Net cash provided by financing activities		612,841	413,973	448,151
Net Change in Cash and Cash Equivalents		(86,182)	(1,100)	217,146
Cash and Cash Equivalents, Beginning of Period		445,701	446,801	229,655
Cash and Cash Equivalents, End of Period		359,519	445,701	446,801
Parent Company
Operating activities:
Net income		54,684	33,127	28,383
Adjustments to reconcile net income to net cash used in operating activities		(44,185)	(26,561)	(25,357)
Net cash provided by (used in) operating activities		10,499	6,566	3,026
Investing activities:
Contributed capital to subsidiary		(101,868)	(31,625)	(23,971)
Other investing activities		189	(295)
Net cash used in investing activities		(101,679)	(31,920)	(23,971)
Financing activities:
Net change in short‑term borrowings				(10,000)
Dividends paid		(7,950)	(6,224)	(4,222)
Proceeds from issuance of common stock		106,245		3,941
Proceeds from issuance of preferred stock			31,581	10,000
Net cash provided by financing activities		98,295	25,357	19,719
Net Change in Cash and Cash Equivalents		7,115	3	(1,226)
Cash and Cash Equivalents, Beginning of Period		158	155	1,381
Cash and Cash Equivalents, End of Period		$ 7,273	$ 158	$ 155