Accumulated Other Comprehensive Income (Loss) - Summary of Changes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	$ 1,303,463	$ 901,657	$ 850,509
Other comprehensive income before reclassifications	(14,870)	12,340
Amounts reclassified from accumulated other comprehensive income	(3,018)	(1,667)	(2,422)
Period change	(17,888)	10,673	(12,219)
Reclassification adjustment under ASU 2018-02	0
Ending balance	1,408,260	1,303,463	901,657
Total
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(2,908)	(13,581)	(1,362)
Period change	(17,888)	10,673	(12,219)
Reclassification adjustment under ASU 2018-02	(626)
Ending balance	(21,422)	(2,908)	(13,581)
Unrealized Gains (Losses) on Securities Available for Sale
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	8,970	1,035
Other comprehensive income before reclassifications	(13,872)	9,645
Amounts reclassified from accumulated other comprehensive income	(3,373)	(1,710)	(2,203)
Period change	(17,245)	7,935
Reclassification adjustment under ASU 2018-02	1,932
Ending balance	(6,343)	8,970	1,035
Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(1,125)	(1,774)
Other comprehensive income before reclassifications	437	9
Amounts reclassified from accumulated other comprehensive income	371	640	813
Period change	808	649
Reclassification adjustment under ASU 2018-02	(242)
Ending balance	(559)	(1,125)	(1,774)
Unrealized Gains (Losses) on Defined Benefit Plans
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(10,753)	(12,842)
Other comprehensive income before reclassifications	(1,435)	2,686
Amounts reclassified from accumulated other comprehensive income	(16)	(597)
Period change	(1,451)	2,089
Reclassification adjustment under ASU 2018-02	(2,316)
Ending balance	$ (14,520)	$ (10,753)	$ (12,842)