Benefit Plans - Changes to Benefit Obligations and Fair Value of Plan Assets and Funded Status (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015
Funded status and amounts recognized in balance sheets
Pension liabilities for underfunded plans					$ (132,904)	$ (133,910)
Pension Benefits
Changes to PBO or APBO
Benefit obligation at beginning of year		$ 203,384	$ 215,684
Service cost		944	809	$ 702
Interest cost		8,784	8,681	8,995
Actuarial (gain) loss		9,653	(8,004)
Benefit payments		(14,061)	(13,786)
Change due to the Reorganization Transactions		703
Benefit obligation at end of year	$ 209,407	209,407	203,384	215,684
Changes to fair value of plan assets
Fair value of plan assets at beginning of year		89,161	96,528
Actual return on plan assets		1,348	478
Contributions		25,953
Benefit payments from trust		(7,912)	(7,845)
Fair value of plan assets at end of year	108,550	108,550	89,161	96,528
Funded status and amounts recognized in balance sheets
Pension assets for overfunded plans					11,618
Pension liabilities for underfunded plans					(112,475)	(114,223)
Funded status					(100,857)	(114,223)
PBO, ABO and fair value of plan assets
Projected benefit obligation	209,407	203,384	215,684	215,684	209,407	203,384
Accumulated benefit obligation					207,157	200,434
Fair value of plan assets	108,550	89,161	96,528	96,528	108,550	89,161
Overfunded (underfunded) portion of PBO/ABO					(100,857)	(114,223)
Other Benefits
Changes to PBO or APBO
Benefit obligation at beginning of year		19,687	19,608
Service cost		697	734	742
Interest cost		812	770	925
Actuarial (gain) loss		(337)	(1,019)
Benefit payments		(430)	(406)
Benefit obligation at end of year	20,429	20,429	19,687	19,608
Funded status and amounts recognized in balance sheets
Pension liabilities for underfunded plans					(20,429)	(19,687)
Funded status					(20,429)	(19,687)
PBO, ABO and fair value of plan assets
Projected benefit obligation	20,429	19,687	19,608	19,608	20,429	19,687
Pension Plan
Changes to PBO or APBO
Benefit obligation at beginning of year		98,261
Interest cost		4,182	4,252	$ 4,461
Benefit obligation at end of year	96,859	96,859	98,261
Changes to fair value of plan assets
Fair value of plan assets at beginning of year		89,161
Contributions	26,000
Fair value of plan assets at end of year	108,550	108,550	89,161
PBO, ABO and fair value of plan assets
Projected benefit obligation	96,859	98,261	98,261		96,859	98,261
Accumulated benefit obligation					96,859	98,261
Fair value of plan assets	108,550	89,161	89,161		108,550	89,161
Overfunded (underfunded) portion of PBO/ABO					11,691	(9,100)
SERP and Directors’ Plan
Changes to PBO or APBO
Benefit obligation at beginning of year		105,123
Benefit obligation at end of year	112,548	112,548	105,123
PBO, ABO and fair value of plan assets
Projected benefit obligation	$ 112,548	$ 105,123	$ 105,123		112,548	105,123
Accumulated benefit obligation					110,298	102,173
Overfunded (underfunded) portion of PBO/ABO					$ (112,548)	$ (105,123)