Condensed Financial Statements of Parent Company - Condensed Statements of Income - (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income:
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest, Total	$ 168,805	$ 154,042	$ 150,375
Applicable income tax benefit	(81,251)	(52,760)	(50,902)
Net income	87,554	101,282	99,473
Net income	87,554	101,282	99,473
Parent company
Income:
Dividends from subsidiaries	63,703	36,328	82,765
Operating income (loss)	580	177	38
Total income	64,283	36,505	82,803
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest, Total	48,801	23,817	73,920
Operating expenses	15,482	12,688	8,883
Applicable income tax benefit	5,053	4,270	2,975
Equity in undistributed earnings of subsidiary (excess distribution)	33,700	73,195	22,578
Net income	87,554	101,282	99,473
Net income	$ 87,554	$ 101,282	$ 99,473