Derivative Instruments - Changes in AOCI (net of tax) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of the period	$ 2,382,589	$ 2,093,126	$ 1,360,412	$ 1,356,692	$ 990,772	$ 1,050,607	$ 1,360,412	$ 1,050,607
Comprehensive income	10,436	(2,280)	(8,470)	(4,724)	(3,842)	(3,751)	(314)	(12,317)
Balance at end of the period	2,358,301	2,382,589	2,093,126	1,372,507	1,356,692	990,772	2,358,301	1,372,507
Derivative gains (losses) recognized in other comprehensive income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of the period	(5,922)	(5,668)	(2,778)	(2,147)	1,698	3,644	(2,778)	3,644
Comprehensive income	(66)	(1,109)	(3,160)	(1,271)	(4,247)	(2,376)
Balance at end of the period	(4,830)	(5,922)	(5,668)	(3,208)	(2,147)	1,698	$ (4,830)	$ (3,208)
Derivative gains (losses) recognized in other comprehensive income (loss) | Amount reclassified out of other comprehensive income (loss) to net loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Comprehensive income	$ 1,158	$ 855	$ 270	$ 210	$ 402	$ 430