Parent Company Only Condensed Financial Statements - Consolidated Statements of Cash Flow (Details) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Adjustments to reconcile net income to net cash provided by operating activities:
Share-based compensation	$ 3,427	$ 3,367	$ 3,601
Excess tax benefit of share-based compensation	0	(1,327)	(449)
Net cash provided by operating activities	45,791	82,521	47,187
Cash flows from investing activities:
Net cash paid for acquisitions and dispositions	4,456	0	0
Net cash used in investing activities	(312,444)	(358,057)	(337,250)
Cash flows from financing activities:
Proceeds from the issuance of subordinated notes	0	48,733	0
Proceeds from Notes Payable	10,000	0	0
Repayments of Notes Payable	10,000	0	5,700
Cash dividends paid	(10,249)	(8,211)	(5,259)
Excess tax benefit of share-based compensation	0	1,327	449
Payments for Repurchase of Common Stock	16,636	4,889	0
Net cash provided by financing activities	221,174	380,181	283,524
Net increase (decrease) in cash and cash equivalents	(45,479)	104,645	(6,539)
Cash and cash equivalents, beginning of period	198,802	94,157	100,696
Cash and cash equivalents, end of period	$ 153,323	$ 198,802	$ 94,157
Noncash transactions:
Stock Issued During Period, Shares, Acquisitions	141,729	0	0
Parent [Member]
Cash flows from operating activities:
Net income available to common shareholders	$ 48,190	$ 48,837	$ 38,450
Adjustments to reconcile net income to net cash provided by operating activities:
Share-based compensation	3,427	3,367	3,601
Net income of subsidiaries	(55,053)	(53,235)	(41,298)
Dividends from subsidiaries	20,000	7,500	10,000
Excess tax benefit of share-based compensation	0	(1,327)	(449)
Other, net	(1,806)	1,848	848
Net cash provided by operating activities	14,758	6,990	11,152
Cash flows from investing activities:
Cash contributions to subsidiaries	0	(250)	0
Net cash paid for acquisitions and dispositions	(25,187)	0	0
Purchases of other investments	(3,679)	(2,435)	(2,832)
Proceeds from distributions on other investments	1,634	1,151	880
Net cash used in investing activities	(27,232)	(1,534)	(1,952)
Cash flows from financing activities:
Proceeds from the issuance of subordinated notes	0	48,733	0
Proceeds from Notes Payable	10,000	0	0
Repayments of Notes Payable	10,000	0	5,700
Cash dividends paid	(10,249)	(8,211)	(5,259)
Excess tax benefit of share-based compensation	0	1,327	449
Payments for Repurchase of Common Stock	16,636	4,889	0
Payments for the repurchase of equity instruments, net	(2,909)	(2,203)	(1,190)
Net cash provided by financing activities	(29,794)	34,757	(11,700)
Net increase (decrease) in cash and cash equivalents	(42,268)	40,213	(2,500)
Cash and cash equivalents, beginning of period	52,245	12,032	14,532
Cash and cash equivalents, end of period	$ 9,977	$ 52,245	$ 12,032
Noncash transactions:
Stock Issued During Period, Shares, Acquisitions	141,729	0	0