Income Taxes - Statutory Federal Tax Rate (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Tax expense at statutory rate									$ 41,775	$ 37,827	$ 25,587
Non-taxable dividend income									0	0	(1,587)
Income from non-controlling interest									0	(1,901)	0
Loss on retirement of preferred stock									0	(1,874)	(7,766)
Valuation allowance									21	33	(13,542)
Other									261	154	132
Income tax expense	$ 15,793	$ 10,529	$ 8,400	$ 7,335	$ 9,912	$ 6,327	$ 13,769	$ 4,231	$ 42,057	$ 34,239	$ 2,824
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent									35.00%	35.00%	35.00%