CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 309,793	$ 261,428	$ 161,907
Other comprehensive income (loss), net of tax:
Net gains (losses) arising during the period	39,262	(22,932)	850
Less reclassification adjustment for net losses (gains) included in net income	119	2,237	(156)
Total	39,381	(20,695)	694
Unrealized gains and losses on derivatives (cash flow hedges)
Net (losses) gains on derivatives arising during the period	(989)	1,874	576
Less reclassification adjustment for net losses included in net income	1,291	2,494	5,028
Total	302	4,368	5,604
Defined benefit pension plan
Net losses arising during the period	(2,561)	(7,151)	(2,722)
Amortization of prior service (credit) cost	(93)	146	191
Amortization of net loss	188	447	248
Total	(2,466)	(6,558)	(2,283)
Other comprehensive income (loss), net	37,217	(22,885)	4,015
Total comprehensive income	$ 347,010	$ 238,543	$ 165,922