Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 22,890	$ 23,395	$ 23,061	$ 22,726	$ 23,211	$ 16,170	$ 15,029	$ 13,910	$ 92,072	$ 68,320	$ 40,554
Other comprehensive income (loss), net of tax:
Unrealized gains (losses) on available for sale securities arising during the period, after reclassifications									17,159	(12,434)	3,165
Change in minimum pension liability, after reclassifications									(4,502)	388	(370)
Change in joint beneficiary agreement liability									0	426	(110)
Other comprehensive income (loss)									12,657	(11,620)	2,685
Comprehensive income									$ 104,729	$ 56,700	$ 43,239