Fair Value of Financial Instruments - Rollforward of Balance Sheet Amounts Within Level 3 Valuation Hierarchy (Details) - Recurring - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other assets
Assets measured on recurring basis, unobservable input reconciliation, calculation [Roll Forward]
Fair value, beginning of period	$ 23,578	$ 27,850	$ 28,874	$ 10,478
Total realized gains included in income	81	188	2,858	625
Changes in unrealized gains/losses included in other comprehensive income for assets and liabilities still held at September 30	0	0	0	0
Acquired	0	0	0	17,062
Purchases	2,455	815	7,273	1,584
Issuances	0	0	0	0
Settlements	(932)	(376)	(1,657)	(1,272)
Transfers out of Level 3	0	0	(12,166)	0
Fair value, end of period	25,182	28,477	25,182	28,477
Total realized gains included in income related to financial assets and liabilities still on the consolidated balance sheet at September 30	81	188	2,858	625
Available-for-sale Securities
Assets measured on recurring basis, unobservable input reconciliation, calculation [Roll Forward]
Fair value, beginning of period	15,290	0	17,029	0
Total realized gains included in income	30	0	90	0
Changes in unrealized gains/losses included in other comprehensive income for assets and liabilities still held at September 30	34	0	(597)	0
Acquired	0	0	0	0
Purchases	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	(1,168)	0
Transfers out of Level 3	0	0	0	0
Fair value, end of period	15,354	0	15,354	0
Total realized gains included in income related to financial assets and liabilities still on the consolidated balance sheet at September 30	$ 30	$ 0	$ 90	$ 0