Interest Rate Contracts - Summary of Interest Rate Swaps (Details) - USD ($)	Jun. 30, 2019	Dec. 31, 2018
Derivative [Line Items]
Fair value of interest rate swap in a net asset (liability) position		$ (1,717,000)
Current Notional Amounts	$ 850,000,000	850,000,000
Interest Rate Swap Effective Date July 9, 2015
Derivative [Line Items]
Interest Strike Rate (percent)	1.69%
Fair value of interest rate swap in a net asset (liability) position	$ 704,000	5,245,000
Current Notional Amounts	$ 425,000,000	425,000,000
Interest Rate Swap Effective Date July 1, 2020
Derivative [Line Items]
Interest Strike Rate (percent)	2.82%
Fair value of interest rate swap in a net asset (liability) position	$ (6,785,000)	(1,987,000)
Current Notional Amounts	$ 125,000,000	125,000,000
Interest Rate Swap Effective Date July 1, 2020
Derivative [Line Items]
Interest Strike Rate (percent)	2.82%
Fair value of interest rate swap in a net asset (liability) position	$ (5,449,000)	(1,628,000)
Current Notional Amounts	$ 100,000,000	100,000,000
Interest Rate Swap Effective Date July 1, 2020
Derivative [Line Items]
Interest Strike Rate (percent)	2.83%
Fair value of interest rate swap in a net asset (liability) position	$ (5,464,000)	(1,636,000)
Current Notional Amounts	$ 100,000,000	100,000,000
Interest Rate Swap Effective Date July 1, 2020
Derivative [Line Items]
Interest Strike Rate (percent)	2.84%
Fair value of interest rate swap in a net asset (liability) position	$ (5,547,000)	(1,711,000)
Current Notional Amounts	100,000,000	$ 100,000,000
Interest Rate Swap
Derivative [Line Items]
Fair value of interest rate swap in a net asset (liability) position	$ (22,541,000)