Parent Company Financial Statements (Condensed Statements of Income and Comprehensive Income) (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
EXPENSES
Salaries and Employee Benefits									$ 46,642	$ 43,961	$ 35,042
Professional Fees									2,817	3,672	2,661
Interest Expense									11,121	8,461	6,068
INCOME BEFORE INCOME TAXES AND EQUITY IN UNDISTRIBUTED INCOME OF SUBSIDIARIES									52,210	49,130	41,670
Income Tax Benefit									(11,534)	(13,946)	(11,606)
NET INCOME	$ 11,621	$ 9,660	$ 9,839	$ 9,556	$ 10,065	$ 10,185	$ 9,788	$ 5,146	40,676	35,184	30,064
Other Comprehensive Income:
COMPREHENSIVE INCOME									44,929	24,968	30,986
Parent Company
INCOME
Interest Income									34	20	30
Other Income (Loss)									25	(27)	21
Total Income									26,034	15,993	17,455
EXPENSES
Salaries and Employee Benefits									533	1,006	500
Professional Fees									602	1,096	739
Occupancy and Equipment Expense									7	13	8
Interest Expense									877	742	491
Other Expenses									794	750	657
Total Expenses									2,813	3,607	2,395
INCOME BEFORE INCOME TAXES AND EQUITY IN UNDISTRIBUTED INCOME OF SUBSIDIARIES									23,221	12,386	15,060
Income Tax Benefit									1,415	1,284	893
INCOME BEFORE EQUITY IN UNDISTRIBUTED INCOME OF SUBSIDIARIES									24,636	13,670	15,953
Equity in Undistributed Income of Subsidiaries									16,040	21,514	14,111
NET INCOME									40,676	35,184	30,064
Other Comprehensive Income:
Changes in Unrealized Gain (Loss) on Securities, Available-for-Sale									4,391	(10,202)	932
Changes in Unrecognized (Loss) in Postretirement Benefit Obligation, Net									(138)	(14)	(10)
COMPREHENSIVE INCOME									44,929	24,968	30,986
Parent Company | Bank
INCOME
Dividends from Subsidiaries									25,000	15,000	15,900
Parent Company | Non-bank
INCOME
Dividends from Subsidiaries									$ 975	$ 1,000	$ 1,504