Disclosure About Fair Values of Financial Instruments - Summary of Changes in Level 3 Assets Measured at Fair Value on a Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Net Profits Interests
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 5,779	$ 15,833
Net gains included in earnings	(174)	(869)
Distributions received	(288)	(669)
Ending Balance	5,317	14,295
Net unrealized gains (losses) included in earnings relating to assets held at the end of the period	(174)	(869)
Investments in Limited Partnerships
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	11,191
Net gains included in earnings	746	676
Reclassifications	(800)
Contributions paid	608	225
Distributions received	(144)	(106)
Ending Balance	11,601	7,514
Net unrealized gains (losses) included in earnings relating to assets held at the end of the period	$ 746	676
Investments in Limited Partnerships | ASU 2016-01
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Transfers in due to adoption of ASU 2016-01		5,518
Adjustment recorded in retained earnings due to adoption of ASU 2016-01		$ 1,201