Noncontrolling Interests Text Details (Details) - USD ($) $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2017		Sep. 30, 2017	[1]	Jun. 30, 2017	[1]	Mar. 31, 2017	[1]	Dec. 31, 2016		Sep. 30, 2016	[1]	Jun. 30, 2016	[1]	Mar. 31, 2016	[1]	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Noncontrolling Interest [Line Items]
Net Income (Loss) Attributable to Noncontrolling Interest	$ 1,278	[1]	$ 1,074		$ 1,150		$ 966		$ 1,147	[1]	$ 1,110		$ 989		$ 911		$ 4,468	$ 4,157	$ 4,407
Redeemable noncontrolling interests	17,461								16,972								17,461	16,972
Nonredeemable Noncontrolling Interest	5,186								4,161								5,186	4,161
Anchor [Member]
Noncontrolling Interest [Line Items]
Nonredeemable Noncontrolling Interest	2,900								2,000								2,900	2,000
Redeemable and Nonredeemable Noncontrolling Interest	9,761								10,934								9,761	10,934
BOS [Member]
Noncontrolling Interest [Line Items]
Nonredeemable Noncontrolling Interest	2,300								2,200								2,300	2,200
Redeemable and Nonredeemable Noncontrolling Interest	8,057								6,782								8,057	6,782
DGHM [Member]
Noncontrolling Interest [Line Items]
Redeemable noncontrolling interests	$ 4,829								$ 3,417								$ 4,829	$ 3,417

[1] Due to rounding, the sum of the four quarters may not add to the year to date total.