Parent Company Only Condensed Financial Statements - Condensed Statements of Operations (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
Operating Income [Abstract]
Dividends from subsidiaries									$ 449	$ 226	$ 141
Operating Expenses [Abstract]
Interest expense-subordinated debentures and notes									5,095	1,894	1,248
Interest expense-notes payable	$ 7,385	$ 6,843	$ 5,909	$ 5,098	$ 3,984	$ 3,463	$ 3,250	$ 3,032	25,235	13,729	12,369
Income tax benefit	(19,820)	(7,856)	(5,545)	(5,106)	(7,053)	(6,316)	(6,747)	(5,886)	(38,327)	(26,002)	(19,951)
Net income	$ 7,529	$ 16,315	$ 11,955	$ 12,391	$ 13,628	$ 11,832	$ 12,352	$ 11,025	48,190	48,837	38,450
Total comprehensive income									46,113	46,878	36,987
Parent [Member]
Operating Income [Abstract]
Dividends from subsidiaries									20,000	7,500	10,000
Other									708	491	249
Total income									20,708	7,991	10,249
Operating Expenses [Abstract]
Interest expense-subordinated debentures and notes									5,094	1,893	1,248
Interest expense-notes payable									89	53	144
Other expenses									5,486	5,526	3,823
Total expenses									10,669	7,472	5,215
Income before taxes and equity in undistributed earnings of subsidiaries									10,039	519	5,034
Income tax benefit									3,098	2,583	2,118
Net income									13,137	3,102	7,152
Equity in undistributed earnings of subsidiaries									35,053	45,735	31,298
Total comprehensive income									$ 48,190	$ 48,837	$ 38,450