Income Taxes - Reconciliation of Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended	12 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Computed expected tax expense				$ 13,044	$ 4,640	$ 681
State income taxes, net of federal tax effect				4,748	(1,129)	6
Changes in state DTL for mergers				0	0	3,320
Excess share based compensation				(1,254)	(3,314)	(1,709)
Nondeductible merger expenses				0	0	801
Revaluation of U.S. deferred income taxes				(760)	(53,449)	0
Other, net				(261)	119	(259)
Income tax expense (benefit)	$ 3,531	$ 1,828	$ 5,359	$ 15,517	$ (53,133)	$ 2,840