Recent Accounting Developments (Narratives) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Jan. 01, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle
Cumulative effect on other comprehensive income		$ 959	$ 2,290	$ 13,141	$ 4,149
ASU 2017-12
New Accounting Pronouncements or Change in Accounting Principle
Cumulative effect on retained earnings						$ 383
ASU 2016-02 | Pro Forma
New Accounting Pronouncements or Change in Accounting Principle
Right-of-use asset, less than		25,000		25,000
Lease liability, less than		$ 25,000		$ 25,000
Accumulated Other Comprehensive Income (Loss)
New Accounting Pronouncements or Change in Accounting Principle
Adjustments related to TCJA	$ (300)
Accumulated Deficit
New Accounting Pronouncements or Change in Accounting Principle
Adjustments related to TCJA	$ 300
Accumulated Deficit | ASU 2017-12
New Accounting Pronouncements or Change in Accounting Principle
Cumulative effect on retained earnings						$ 383