Equity - Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 644,729
Income tax expense		$ (185)	$ 630
Net other comprehensive income (loss)	(31,950)	2,572	(1,332)
Transition adjustment related to adoption	219,817	644,729	469,577	$ 378,156
Ending balance	205,301	644,729
AOCI Attributable to Parent [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(28,159)	(28,024)	(26,692)
Gains (losses) arising during period	(42,859)	4,232	(2,231)
Amounts reclassified from accumulated other comprehensive loss	10,909	(1,475)	269
Income tax expense		(185)	630
Net other comprehensive income (loss)	(31,950)	2,572	(1,332)
Transition adjustment related to adoption	(57,951)	(28,159)	(28,024)	$ (26,692)
Ending balance	(57,951)	(28,159)	(28,024)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(23,916)	(21,814)	(20,149)
Gains (losses) arising during period	(2,901)	693	(2,231)
Amounts reclassified from accumulated other comprehensive loss	194	97	(64)
Income tax expense		(185)	630
Net other comprehensive income (loss)	(2,707)	605	(1,665)
Ending balance	(26,623)	(23,916)	(21,814)
Accumulated Other-than-Temporary Impairment Attributable to Parent [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(5,877)	(6,210)	(6,543)
Amounts reclassified from accumulated other comprehensive loss	210	333	333
Net other comprehensive income (loss)	210	333	333
Ending balance	(3,509)	(5,877)	(6,210)
Interest Rate Derivatives
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	1,634
Gains (losses) arising during period	(39,958)	3,539
Amounts reclassified from accumulated other comprehensive loss	10,505	(1,905)
Net other comprehensive income (loss)	(29,453)	1,634
Ending balance	(27,819)	1,634
Cumulative Effect, Period of Adoption, Adjustment [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Transition adjustment related to adoption	(3,185)		$ (134)
Cumulative Effect, Period of Adoption, Adjustment [Member] | AOCI Attributable to Parent [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Transition adjustment related to adoption	2,158	(2,707)
ASU 2018-02 [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member] | AOCI Attributable to Parent [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Transition adjustment related to adoption		(2,707)
ASU 2018-02 [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member] | Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Transition adjustment related to adoption		$ (2,707)
ASU 2016-13 [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member] | AOCI Attributable to Parent [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Transition adjustment related to adoption	2,158
ASU 2016-13 [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member] | Accumulated Other-than-Temporary Impairment Attributable to Parent [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Transition adjustment related to adoption	$ 2,158