Parent Company Financial Statements (Statements of Income) (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
Condensed Financial Statements, Captions [Line Items]
Dividend income from subsidiary									$ 1,100,000	$ 1,000,000	$ 579,000
Interest on borrowings									5,585,000	4,506,000	3,457,000
Income before income tax expense	$ 16,162,000	$ 16,817,000	$ 14,955,000	$ 14,420,000	$ 15,632,000	$ 15,945,000	$ 13,874,000	$ 12,088,000	62,354,000	57,539,000	30,859,000
Income tax (expense) benefit	(19,335,000)	(5,478,000)	(4,721,000)	(4,344,000)	(4,730,000)	(5,042,000)	(4,258,000)	(3,442,000)	(33,878,000)	(17,472,000)	(9,907,000)
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
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Dividend income from subsidiary									16,800,000	16,000,000	39,200,000
Other income (loss)									145,000	239,000	(18,000)
Total operating income									16,945,000	16,239,000	39,182,000
Interest on borrowings									3,408,000	3,415,000	2,734,000
Fees to Bank									160,000	160,000	160,000
Other operating expenses									592,000	748,000	469,000
Total operating expenses									4,160,000	4,323,000	3,363,000
Income before equity in undistributed earnings of subsidiaries and income taxes									12,785,000	11,916,000	35,819,000
Equity in undistributed income (losses) of subsidiaries									17,405,000	26,773,000	(15,999,000)
Income before income tax expense									30,190,000	38,689,000	19,820,000
Income tax (expense) benefit									(1,714,000)	1,378,000	1,132,000
Net income									$ 28,476,000	$ 40,067,000	$ 20,952,000