Goodwill and Intangible Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Goodwill [Line Items]
Goodwill	$ 530,593,000	$ 530,593,000
Non-amortizing intangible assets	963,000	963,000
Balance at end of year	531,556,000	531,556,000
Goodwill impairment charges	0	$ 0	$ 0
Subsidiaries | Six Reporting Units
Goodwill [Line Items]
Goodwill	$ 530,600,000
Goodwill impairment test fair value exceeding adjusted net book value	62.00%