Parent Company Financial Statements (Statements of Cash Flows) (Details) - USD ($)	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
Operating Activities
Net income	$ (3,173,000)	$ 11,339,000	$ 10,234,000	$ 10,076,000	$ 10,902,000	$ 10,903,000	$ 9,616,000	$ 8,646,000	$ 28,476,000	$ 40,067,000	$ 20,952,000
(Increase) decrease in other assets									12,060,000	11,836,000	(7,062,000)
Net cash provided by operating activities									58,334,000	58,510,000	15,918,000
Investing Activities
Net cash used in investing activities									(212,131,000)	(169,045,000)	(54,744,000)
Financing Activities
Issuance of subordinated debt, net of issuance costs									0	0	14,464,000
Exercise of stock options and issuance of restricted stock, net of repurchase for tax withholdings									606,000	(894,000)	(753,000)
Equity issuance costs									0	0	(612,000)
Cash dividends paid on common stock and cash in lieu for fractional shares paid due to stock split									(14,323,000)	(12,394,000)	(9,785,000)
Net cash provided by financing activities									169,061,000	118,754,000	57,501,000
Net increase in cash and cash equivalents									15,264,000	8,219,000	18,675,000
Cash and cash equivalents at beginning of year				87,707,000				79,488,000	87,707,000	79,488,000	60,813,000
Cash and cash equivalents at end of year	102,971,000				87,707,000				102,971,000	87,707,000	79,488,000
Parent Company [Member]
Operating Activities
Net income									28,476,000	40,067,000	20,952,000
Equity in undistributed (income) losses of subsidiaries									(17,405,000)	(26,655,000)	4,573,000
Gain on sale of investment securities									(32,000)	(4,000)	0
(Increase) decrease in receivable from subsidiaries									0	1,819,000	(1,901,000)
(Increase) decrease in other assets									(1,930,000)	1,213,000	(2,175,000)
Increase (decrease) in due to subsidiaries									(20,000)	(1,179,000)	1,216,000
Increase (decrease) in other liabilities									3,721,000	(2,519,000)	320,000
Net cash provided by operating activities									12,810,000	12,742,000	22,985,000
Investing Activities
Acquisition of SBM, net of cash acquired									0	0	(25,319,000)
Proceeds from Sale of Available-for-sale Securities, Equity									110,000	84,000	0
Net cash used in investing activities									110,000	84,000	(25,319,000)
Financing Activities
Issuance of subordinated debt, net of issuance costs									0	0	14,464,000
Exercise of stock options and issuance of restricted stock, net of repurchase for tax withholdings									606,000	(894,000)	(753,000)
Capital contribution from subsidiaries									1,469,000	1,997,000	836,000
Equity issuance costs									0	0	(612,000)
Cash dividends paid on common stock and cash in lieu for fractional shares paid due to stock split									(14,323,000)	(12,393,000)	(9,785,000)
Net cash provided by financing activities									(13,460,000)	(9,502,000)	5,656,000
Net increase in cash and cash equivalents									(540,000)	3,324,000	3,322,000
Cash and cash equivalents at beginning of year				$ 29,905,000				$ 26,581,000	29,905,000	26,581,000	23,259,000
Cash and cash equivalents at end of year	$ 29,365,000				$ 29,905,000				$ 29,365,000	$ 29,905,000	$ 26,581,000