Equity (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			$ 148,732
Stock based-awards			12,392
Repurchase of common shares			(3,960)
Dividends paid			(48,635)
Amortization of deferred pension costs, net of tax			97
Interest rate swaps, net of tax			766
Net income	$ 24,805	$ 22,709	48,382	$ 40,391
Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest	53	$ 19	103	$ 43
Ending balance	157,774		157,774
Common Shares
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			1,148
Stock based-awards			0
Repurchase of common shares			0
Dividends paid			0
Amortization of deferred pension costs, net of tax			0
Interest rate swaps, net of tax			0
Net income			0
Ending balance	1,148		1,148
Additional Paid-In Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			54,463
Stock based-awards			4,464
Repurchase of common shares			0
Dividends paid			0
Amortization of deferred pension costs, net of tax			0
Interest rate swaps, net of tax			0
Net income			0
Ending balance	58,927		58,927
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			173,855
Stock based-awards			0
Repurchase of common shares			0
Dividends paid			(48,635)
Amortization of deferred pension costs, net of tax			0
Interest rate swaps, net of tax			0
Net income			48,279
Ending balance	173,499		173,499
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			(8,353)
Stock based-awards			0
Repurchase of common shares			0
Dividends paid			0
Amortization of deferred pension costs, net of tax			97
Interest rate swaps, net of tax			766
Net income			0
Ending balance	(7,490)		(7,490)
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			(76,269)
Stock based-awards			7,928
Repurchase of common shares			(3,960)
Dividends paid			0
Amortization of deferred pension costs, net of tax			0
Interest rate swaps, net of tax			0
Net income			0
Ending balance	(72,301)		(72,301)
Non-Controlling Interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			3,888
Stock based-awards			0
Repurchase of common shares			0
Dividends paid			0
Amortization of deferred pension costs, net of tax			0
Interest rate swaps, net of tax			0
Ending balance	$ 3,991		$ 3,991