Consolidated Statements of Changes in Stockholder's Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in-Capital	Retained Earnings	Accumulated Other Comprehensive (Loss), Net of Tax	Common Stock Held by the Employee Stock Ownership Plan	Stock Held by Rabbi Trust	Deferred Compensation Obligation
Balance at beginning of period at Dec. 31, 2017	$ 472,070	$ 0	$ 0	$ 537,480	$ (65,410)	$ 0	$ 0	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	11,784			11,784
Other comprehensive income (loss)	(9,949)				(9,949)
Balance at end of year at Mar. 31, 2018	473,905	0	0	549,264	(75,359)	0	0	0
Balance at beginning of period at Dec. 31, 2018	972,060	1,159	527,037	560,216	(71,897)	(43,835)	(1,259)	639
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	14,919			14,919
Other comprehensive income (loss)	6,625				6,625
Employee Stock Ownership Plan shares committed to be released	868		309			559
Funding of deferred compensation obligations	30						(100)	130
Balance at end of year at Mar. 31, 2019	$ 994,502	$ 1,159	$ 527,346	$ 575,683	$ (65,820)	$ (43,276)	$ (1,359)	$ 769