Other Comprehensive Income (Loss) - Changes in components of other comprehensive income (loss) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 961,126	$ 994,502	$ 982,517	$ 972,060
Current period changes in other comprehensive income (loss)	6,458	4,501	15,528	11,126
Balance at end of year	1,040,988	1,007,909	1,040,988	1,007,909
Accumulated Other Comprehensive (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(59,665)	(65,820)	(68,735)	(71,897)
Current period changes in other comprehensive income (loss)	6,458	4,501	15,528	11,126
Balance at end of year	(53,207)	(61,319)	(53,207)	(61,319)
Unrealized Gains on Debt Securities Available for Sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	28,875	(4,369)	9,313	(13,226)
Current period changes in other comprehensive income (loss)	6,350	14,350	25,912	23,755
Balance at end of year	35,225	9,981	35,225	9,981
Unrealized (Losses) on Swaps
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(19,823)	(4,786)	(8,474)	(2,006)
Current period changes in other comprehensive income (loss)	(750)	(4,676)	(12,099)	(7,456)
Balance at end of year	(20,573)	(9,462)	(20,573)	(9,462)
Employee Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(68,717)	(56,665)	(69,574)	(56,665)
Current period changes in other comprehensive income (loss)	858	(5,173)	1,715	(5,173)
Balance at end of year	$ (67,859)	$ (61,838)	(67,859)	(61,838)
Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period				0
Cumulative Effect, Period of Adoption, Adjustment | Accumulated Other Comprehensive (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period				(548)
Cumulative Effect, Period of Adoption, Adjustment | Unrealized Gains on Debt Securities Available for Sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period				(548)
Cumulative Effect, Period of Adoption, Adjusted Balance
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period				972,060
Cumulative Effect, Period of Adoption, Adjusted Balance | Accumulated Other Comprehensive (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			(68,735)	(72,445)
Cumulative Effect, Period of Adoption, Adjusted Balance | Unrealized Gains on Debt Securities Available for Sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			9,313	(13,774)
Cumulative Effect, Period of Adoption, Adjusted Balance | Unrealized (Losses) on Swaps
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			(8,474)	(2,006)
Cumulative Effect, Period of Adoption, Adjusted Balance | Employee Benefit Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period			$ (69,574)	$ (56,665)